Why is 都 placed after a verb in "什么时候还都可以"? I found this example:

你拿着用吧，什么时候还都可以。
Nǐ ná zheyòng ba, shénme shíhòu huán dōu kěyǐ.
You can have it as long as you want.

I am confused about the grammar structure behind 什么时候还都可以 (literally: any time you return it is ok). How is it possible 都 occurs after the verb 还 (to return)? Until now, I always saw 都 before any verb.
In the sentence 什么时候还都可以

the subject is 什么时候还 (the topic in topic-comment theory)
the predicate is 都可以

可以 is 中心词 (key word or main verb), 都 is an adverb that modifies 可以.