Hey there, I think reality checks for me happen after I'm already aware (or semi-aware) that I'm dreaming. Usually it's just to really make sure and to prove it to myself that I'm in a dream.

I think the other thing with reality checks is that when you do them enough during the day, then that behaviour will follow into your dreams, and increases the chances of you questioning your suroundings at random points. I think the more important part of reality checks is the questioning of reality, rather than the reality check itself (if that makes any sense what so ever.)

Sorry if that confuses you more!
Good luck!