に when to use it?

hi people, here is my first thread.

i have learned so far (thanks to the book nihongo minasan) that に is used to express time when an action is being executed. And is used with verbs involving an immediate and short action. and should be used only when the time contains a number. with that in mind i still don't understand (in the same book) the following sentences

わたしは 9じから 5じまで はたらきます。i assume here you don't use "に" cause it not an immediate and short action but everyday action

but here is the following sentence

まいあさ わたしは 6じに おきます。why use "に" here since in the previous sentence we didn't use it. They both involve time and have numbers. Plus the second sentence is also an everyday action so why here.

same problem with the for the following sentences

ぎんこうは なんじから なんじまでですか。

and

まいばん なんじにねますか。

why is it ok with one and not the other. When do you really know when to use に are these sentences just exceptions?

thanks in advance.

ps: only reply if you know why に wasn't used here don't just copy paste some grammar rules from a book you have.

おねがいします。

You framed your question as "why not に" but it's not just about taking に out of the sentence. Have you considered what function から and まで have here? Is that not discussed in the book you have?

わたしは 9じから 5じまで はたらきます - a range of times. I work from （から） 9 until (まで） 5.
まいあさ わたしは 6じに おきます - a single time. I get up at six.

The same with the other. から and まで can also be used separately, not as a pair. まで is used with に together when you're talking about a range with a fixed endpoint (deadline):

11じに かえります
= be home at eleven (on the dot)
11じまでに かえります
= be home by 11 (possibly before then, 11 is the latest)