When someone you're managing does something whack, I think you need to address it within 24 hours. Ideally, you want to be able to address it immediately, but sometimes emotion overrides logical thinking shortly after the event occurs and we are well-served by a night of sleep.
Allowing it to pass is like encouraging a wound to fester. It gets worse, and it can really hurt the relationship. The sooner you tackle the tough conversation the better, to the extent that you can see the situation objectively.