I think the difference between the two types of examples that you've exhibited is the relative placement in time of the action in the "if" clause, and the action in the other clause.
- If it rains in the evening, we won't go for a walk - here, the event of raining occurs BEFORE the decision about whether to go for a walk.
- My teeth will rot if I eat too much sugar - presumably, I'll be eating the sugar BEFORE my teeth rot.
- If it will significantly increase complexity, don't implement this feature - here, the increasing of complexity occurs AFTER the implementation of the feature.
- I will give you money if it will make you happier - here, you becoming happier occurs AFTER I give you the money.
In all the cases where the "if" part happens first chronologically, we use the present tense. In the cases where the "if" part happens second, we use the future tense. However, because sentences of the first type are far more common than sentences in the second type, a good rule for learners to adopt is "don't use the future tense with IF".
The answer to your second question is that the sentence is just fine as it stands. “When will you be here?” and “What time will you be here?” are perfectly equivalent in all registers. The extra at sounds overly verbose and cumbersome. I would not call it “wrong”, but neither would — well, or should — anyone mark wrong a sentence without it.
The answer to your first question depends on who is doing the questioning and who is doing the answering. I am pretty sure at the fourth-grade level, they are not attempting to teach inflectional morphology. Rather, they just want to know whether the student can tell the difference between a sentence that refers to past events, to present events, or to future events. This is the only distinction that matters for a fourth grader (and arguably, for 99.9998% of the rest of the populace as well). What terminology they use is really not important.
They are asking at what time the parents will be able to meet with them on Tuesday. In that, it is asking about a time in the future, as the use of Tuesday clearly gives away. Therefore, I am sure that is the answer they want to hear. They are not asking about events in the past. They are not asking about events in the present. That leaves only one possibility, and that is in the future.
So that is the answer, and the fourth graders can go home now.
That is because the only super-ultra-fussy-correct answer is one that will do your daughter no good whatsoever, for it will in all likelihood be adjudged the wrong answer by her teacher:
The word can is a present tense modal auxiliary (one whose past tense form is could) which is here used to express time in the future, something that has not yet come to pass.
The word meet is a bare infinitive, and as such has no tense at all. that’s because only finite verb forms can have tenses, not non-finite ones. Although meet looks just the same as the unmarked present tense, this use of meet should not be thought of as being in the present tense. It is not. It is not in any tense at all. It is a bare infinitive.
Because the modal can is already in use for “to be able to”, we cannot then apply the more typical future-indicating modal of will atop what it is already there, since double modals are forbidden in Standard English (and will can sounds wrong in any version I am familiar with). So it has to stand for the future even though it is a present tense form. This is no longer true with “will be able to”, which is why I rephrased it that way.
Of course, one can also express the future via the present tense alone, as in “When are you able to meet with us on Tuesday?” But if I asked a fourth-grader whether that entire question was asking about the past, about the present time, or about a future time, I would mark it wrong if they gave me any answer other than future. Because in fact, it would be wrong to give any other answer to that question.
These are fourth graders, please remember!
English is perfectly capable of expressing actions in the past, the present, and the future. That is all that is being asked here. For the viewpoint of a professional linguist on this and related matters, please see this answer.
Here is the OED’s definition of the word tense:
Gram. Any one of the different forms or modifications (or word-groups) in the conjugation of a verb which indicate the different times (past, present, or future) at which the action or state denoted by it is viewed as happening or existing, and also (by extension) the different nature of such action or state, as continuing (imperfect) or completed (perfect); also abstr. that quality of a verb which depends on the expression of such differences.
Notice what they say about “or word-groups”. A tense can be expressed by word groups. So when I say I will be able to meet you on Tuesday, I am using the word group “will be” to express time in the future. That therefore is a use of future tense by the “or word-groups” definition given above in the OED.
Now, morphologically speaking, there actually is something else going on here, but that is not going to be the sort of answer to feed a fourth-grader. You will just confuse her and annoy her teacher, and possibly the other way around as well, if you make that attempt.
Best Answer
Short answer: Yes, of course English has future tense ... for everyone except the most technical, and for them it doesn't have a future tense because they define "have a tense" in a non-intuitive way. So you can go ahead and say confidently that English has future tense.
Longer answer:
Most everybody (within the monolingual English speaking community) thinks of "I will do that" or "I am going to do that" are unequivocally future tense. It would be perverse to think otherwise; both those sentences describe a situation that occurs in the future. That's how most people, school teachers, newspaper editors, newspaper readers, most everybody thinks. And that is correct. For the majority of people.
However, language scholars, that very small set of expert thinkers who tend see a lot more theoretically of English and also of other languages, use that phrasing differently. "X has a Y tense" is technical terminology that means "The language X has verb forms that inflect for the Y tense". That is, the verb form itself is modified rather than having extra words around it to convey the tense. You have to use 'will' or 'going to'. English can express future tense grammatically (with 'will'), but technically it doesn't 'have' a future tense (assuming that what is meant is 'future tense inflections'). 'Will' is definitely a grammatical marker for future time. 'Going to' is less definitely a grammatical marker, it might be more accurately and technically referred to as a periphrastic future.
I think that a less misleading way for more pedantic people to express it would be to say that English has only two inflected tenses. That way both insiders and outsiders to the technical community of linguists would both know what is going on.
As to your specific examples, the way you label them doesn't really correspond to what anybody else says, informally or formally. I think you may be taking things too literally, or choosing one aspect of a definition out of the expected context.
This is not present tense, it is future, whether 'tomorrow' is mentioned or not.
Yes, This is present tense. Present continuous. You are in the middle of the action of traveling to the bathroom (or in AmE, it is a euphemism for in the middle of the action of micturating or defecating).
This is totally valid English grammar. The use of tomorrow changes the interpretation of 'going' from 'traveling' to the marker of the future. Or it could be interpreted as a contraction of "I am going to go to school", explicitly the future of 'traveling'
Totally correct usage. Ambiguous tense, but not ambiguous meaning.
Obviously wrong. Whether present or future, 2 years ago is contradictory, being in the past.
You might wonder why 'will' isn't considered to definitively say that "English has a future tense" (in the pedantic sense that is. In the less fully formal sense it totally says that English has a future tense). 'Will' is syntactically in the category of 'modal verbs', can may must should etc. Its meaning is certainly future time, but syntactically it is a helper (auxiliary) verb. But pedantically, 'will' is not grammatically about tense (I find this reasoning a bit of a stretch, but that's what being pedantic does).
To compare, French can express the future by either "Je verrai la peinture" (I will see the painting = I see-future the painting) or "Je vais voir la peinture" (I am-going to-see the painting). The first one is a true future tense by having an altered root and an inflection, the second expresses the future by a separate word (just like the English 'going to'). English doesn't have a corresponding inflected form for the future. So linguists say 'French has a future tense but English does not have a future tense'. That's just strange sounding technical language for linguists.
This might seem like cavilling (isn't all technical pedantic terminology there to cavil?) but it is useful terminology for language comparison. Some languages inflect for all tenses, and some don't have any inflections for any grammatical function.
Chinese, for example, is said to have no tense at all. You might wonder how they convey information. How do they wake up in the morning? How do they tie their shoes? Oh my god the Chinese are so inscrutable, with no sense of time they see past and future at once like those aliens in that movie and it's so beautiful and sad at the same time and etc etc
That is of course nonsense. What is the case is that verbs in Chinese (Mandarin) do not inflect for tense at all (or for anything), but they can just as easily express the time of something happening by using ... it's going seem stupid when I say it... it's so obvious... words for time. 'Now', 'next week', 'before my parents met'.
Also, people aren't idiots; context can help determine the sense. Suppose you can't hear how 'die' is conjugated in 'When my great-grandfather [die]' . Did that happen in the past, or in the future? If I am telling you this from my retirement home, it probably happened in the past. If I am visiting a nursing home, it's probably in the (near) future.
Here's a weird thing about English. Consider the sentence "I visit the park on Saturdays". There's no tense there, there's no inflection. But it means that you often go to the park in the past and will likely do so in the future. How do they know when exactly they're doing something? Is anything specified at all? How do they wake up in the morning? Oh my god the English are so inscrutable, how can they know anything, they are timeless and can see equally into the past and the future like time travelers it's so beautiful and sad at the same time etc etc