Anytime you’re being yourself (within reason of course).
I recently had a situation where I considered apologising. In the end I didn’t.
Instead of saying ‘I’m sorry’, I clarified my thoughts on the situation with the other person. You see after giving it some thought I realised that an apology didn’t feel like the right thing to do.
Granted, I didn’t like how the situation turned out initially but it served as a learning curve, a growth point that I needed to experience.
In the grand scheme it was a small-scale misunderstanding, not something worth regretting.