Saying that some action is optional

Question

I am trying to find phrase or word which would properly cover following statement:

You can bring back the book tomorrow if you like, and if not it is fine.

I am trying to find a way to same that some action is optional, and if not done it will not have repercussions including hurt feelings. Hope my question makes sense.

Edit: a better explanation is that I am looking for a word similar to optional but implying it must be done in the future; that it can be procrastinated.

Answer 1

Two other common phrases:

Return the book at some point in the future.

Return the book at your leisure/convenience.

Answer 2

A single word used colloquially, but not in writing, is whenever.

Bring the book back whenever.

This is understood to mean "whenever you like" (which is how it would appear in writing).

Answer 3

‘You can bring back the book tomorrow if you want to, but I’m really in no hurry for it. Keep it for as long as you like.’