Learn English – the order of several adverbs of time

One problem is that the entire concept of "part of speech" is very old. How we use it in English, especially in dictionaries, goes back to the study of Latin and Greek. In this view of English grammar "adverb" is the catch-all category where everything that doesn't fit into one of the other traditional categories ends up. (The others being noun, verb, adjective, pronoun, preposition, conjunction, and interjection.)

Now there is no one, true description of any language (except perhaps constructed languages such as yours). There are merely alternative or competing descriptions which appear over time as more independent analyses of the language are undertaken. Such descriptions or analyses may be called "grammars".

Most (but not all) grammars include a concept of word class under one name or another. So one problem is that "part of speech" has two meanings. One is the specific set of eight categories from the classical languages, the other is as a synonym for word class, which is a lot looser.

So all your example words are adverbs under this older stricter view of parts-of-speech, but their qualities and quirks can be much more thoroughly investigated in newer ways. And various new ways will have various new terms for the classes they put these various words into.

Unless you are inventing a new language specifically to embrace the classical parts of speech you don't have to worry in which they belong, but if you are inventing a new language to learn more about how language works then it will be worth your time reading up on the many newer grammars and language descriptions and analyses.

Yes - I can't find anything grammatically wrong, but certainly your second example doesn't sound natural. It's probably, as you imply, that a lot of information is being condensed into a small space, when it might be better put in extended constructions (get a move on with those prepositional phrases!) or even more than one sentence.

She waited outside this morning.

She waited impatiently outside.

??She waited impatiently this morning.

She waited impatiently outside the school this morning.

She waited - impatiently - outside, this morning.

She waited outside this morning. Impatiently.

Of course, there are some who would say that outside is an intransitive preposition in your second example (and in four of mine).

I've found an article covering 'the Royal Order of Adverbs' at the Farlex Grammar Book. Here are some salient points:

What is the order of adverbs?

Because adverbs are used to modify verbs, adjectives, other adverbs, phrases, clauses, or even entire sentences, they are able to function nearly anywhere in the sentence, depending on their type and what it is they are modifying.

If we use more than one adverb to describe a verb, though, there is a general order in which the different categories of adverbs should appear—this is known as the order of adverbs (sometimes called the royal order of adverbs):

1. Manner

2. Place

3. Frequency

4. Time

5. Purpose

Of course, it is uncommon to use five adverbs in a row to modify the same word, but if a sentence uses two or three, then it is best to follow this order to avoid sounding unnatural....

(*Note: For the sake of conciseness, both single-word adverbs and adverbial phrases will be referred to together as “adverbs” throughout this section.) ...

[I]if we were to make a sentence with all five categories of adverbs together, it might look like this:

“I have to run quickly (manner) down the street (place) each morning (frequency) after breakfast (time) in order to catch my bus to school (purpose).”

Even though the string of adverbs is unusually long, the sentence still sounds smooth and logical because the order is correct. Now let’s try rearranging the order of the adverbs:

“I have to run each morning (frequency) quickly (manner) after breakfast (time) in order to catch my bus to school (purpose) down the street (place).”

By changing the order of the adverbs, we’ve actually changed the meaning of the sentence, or at least made the original meaning nearly incomprehensible. This is especially apparent with the adverbial phrase of purpose 'in order to catch my bus to school'— by placing it before the adverb of place, it now sounds as though it’s the school that’s down the street. There is not such a drastic shift in meaning for the adverbs of frequency, manner, and time, but they still sound awkward and unnatural in the new order.

When we can change the order

There is a great deal of flexibility regarding where in a sentence an adverb can appear, regardless of its content and the rules of order that we looked at above. While the order of adverbs is useful to keep in mind, it is a guide, rather than a law.

..........

Multiple adverbs of the same category

When we use multiple adverbs of the same category to modify the same verb, we order them based on how specific the information is that they provide. For example:

“On my father’s ranch (place), I often (frequency) helped gather the animals at the end of the day (specific time) when I was younger (non-specific time).”

“I lived at home (more specific place) with my parents (less specific place) to save money (purpose) while I was working on my doctorate (time).”

And if the Royal Order ruling has to be seen as a rule of thumb, it is almost inconceivable that this codicil is more binding.