Should the use of apostrophes be consistent?

It is time to rock, but don't be too loud.

Is it recommended to stay consistent with the use of apostrophes? Should it instead be:

It's time to rock, but don't be too loud.

If that is fine either way, what about using the same words with and without apostrophes such as do not and don't?

Words like it's and don't are called contractions. There's no rule or reason why you should either contract all possible phrases in a sentence, or else keep them uncontracted. In fact, I read your examples several times before I figured out the difference between them. It's fine either way, and the same goes for don't/do not.

That said, there are some times when a contraction has a slightly different flavor than its uncontracted counterpart. Don't is an example of this, sounding more colloquial and less stilted in informal speech than do not.