Well, here is how you can tell those sentences in a formal way. Note that there could be many ways but I'm writing what I find closest.
You don't say - used when you agree with someone, or surprised, or utter this in sarcastic way.
"His behavior is very strange." - Yeah! I agree (agreeing).
"Jack won the championship." - Ah, did he? Don't tell me (surprising).
"You know, there's no sun in the night." - Wow, I never knew that! (sarcastic).
Challenge accepted - the speaker is ready to accept the tough task that you think is not possible.
"It's impossible to finish this task by 1800 hr." - Do you think so? Well, I'll do [finish] it.
Bitch Please - A response used when someone says something stupid or when somebody tries stupid on you
"...so you understand the scheme? If you give me 100 bucks, I'll make it double in a week." - Ah, come on! Stop this.
RIP [somebody] - Rest In Peace. This is said when a person has died and you pray that their soul rest in peace - This is abbreviation rather than informal way of expressing grief. You may use the whole phrase and it's okay.
However...
RIP [something] - a tongue in cheek comment when something is no more in the market, internet or the like - Here, you don't need to be formal.
Check this -
So you have two choices:
Not after midnight.
Not until midnight.
After: later than something; following something in time
Until : up to the point in time or the event mentioned
If you say "Not after", you are saying that the restaurant doesn't close later than midnight. It could close any time before midnight, so you haven't answered the question "What time does the restaurant close?". You have said when it doesn't close.
If you say "Not until", you are saying that the restaurant doesn't close up to the time of midnight, then at midnight, it closes. That does answer the question "What time does the restaurant close?".
Best Answer
The most common idiomatic phrase is "What time is it?" If you don't have a specific reason to say something different, you should simply say, "What time is it?"
"What's the time?" is also correct, but maybe slightly less common. ("What is the time?" sounds slightly stilted and foreign to native speakers.)
Other idiomatic phrases might be "Hey, Steve, what time do you have?" or "Hey, Steve, do you have the time?" or "Hey, Steve, do you know the time?"
Source: I am a native US English speaker, born and raised in New York City.