Don't stay up too late!
2. It's time for bed.
It's time for bed.
3. Why haven't you slept?
Why don't you sleep?
You should go to bed early.
You should go to bed early.
You should go to bed early.
You should go to bed early.
6. Go to bed.
Go to sleep!
7. Let's go to bed early.
Let's go to bed early!
8. It's time for bed.
It's time for bed.
Note: hit the sack can only mean going to bed at night after a day's work and study, and taking a nap can't be expressed by this phrase.
9. You should go to bed early and get up early.
You should go to bed early and get up early.
Note: Going to bed early and getting up early means getting into the habit of going to bed early and getting up early. You can't use this phrase when you get up early occasionally.