Using the present tense for future events indicates certainty, consistency, and familiarity. In other words, use this to talk about events which will happen, which happen on a regular basis (or are predictable in some way), and about which you have some personal knowledge.
The holidays start next week.
I know this happens every year, last year I saw it happen in the same way, and I am sure it will happen the same way this year.
The train leaves in five minutes
I know the train leaves at a specific time, I know that trains usually leave on time, and I have seen the schedule to confirm when the train will leave.
The gala event starts tomorrow
I have personal knowledge that it is scheduled for tomorrow, I know that events like this usually start on schedule, and I feel comfortable asserting that it will definitely happen.
If any of these three does not exist, there is uncertainty, and the future tense will be more appropriate.
We get paid on Friday
I know this happens with some consistency and regularity, as I've already received at least one paycheck on Friday.
We will get paid on Friday
Oops, now there is some doubt. I hope this will happen, but I'm not sure it'll happen.
Here's another example: given no other context, consider these two sentences:
He will make the winning shot of the game in twenty seconds.
He makes the winning shot of the game in twenty seconds.
The first indicates a future condition, but the context is unclear. Do I really know this will happen? Probably not. More likely I'm expressing an opinion, or a personal hope.
But the second sentence, that expresses an odd certainty. The context is either that we are watching a recording of the game which I have seen before, or that I'm psychic, and I've already seen this happen with my mental powers.
In that specific context, we'd actually say, "I can't hear you," since we know "you" are speaking. "I don't hear" may indicate that there is no sound to be heard: I don't hear anyone out there.
In general, both the simple present and the present progressive forms of sense verbs are used. Often the difference between them is only the difference you'd expect from the tenses - one (progressive) describes an ongoing event, the other (simple present) a habit, or an event that's not time-bound:
Do you see that? // Are you seeing this?
If I hear you say... // If I'm hearing you correctly...
She feels the soft grass // The kids are feeling the animals in the touch tank
The cook smells the soup // While the dog is smelling all the other dogs...
He tastes cardamom in the coffee // As the diners are eating, they're tasting all the flavors in the food
Best Answer
There is a "connector" after time. But it's been omitted.
Both
and
are idiomatic and grammatical.
Notice that the relative pronoun that can be omitted without changing the meaning. I've indicated the relative clause in italics.
See Cambridge on Relative pronouns, including Relative pronouns: that and No relative pronoun, the latter of which talks about omitting the relative pronoun.
See Omission of that on the website English Grammar.
Related: Omission of "that" in this text, which seems to be partially based on/inspired by English Grammar (the first result in a Google search for 'Omission of that').