Suppose you need to call someone who's in college, and they get 3-4 breaks between classes on a regular college day. And you say
I know what times your breaks are, I'll call you while you're on one of those breaks.
Is the above sentence grammatically correct?
Would it be better if I had used when your breaks are..., instead of what times? Do we use time even when talking about different times? I ask this because, we're talking about how the person gets 3-4 breaks at different times.
I read in some grammar book how it's okay to leave out the "at" when constructing sentences like the one I've used, when having an informal conversation.