when do you know it's time to leave a place
measure where you are now, with the possibilities you see everyday. Not just the possibilities you want, but all possibilities you can take ("the soup"). If where you are now outranks most of the soup, then I say "stay".
If you have to jump, make sure it's not into the abyss of possibility soup
When I dread going back to it. But I suppose that's only a useful metric if you can leave temporarily.
For me it's after three consecutive affirmative Magic 8 Ball answers -OR- when my wife tells me it is. :-)
Apart from practical issues (money, time) I'd offer when it affects your Demeanour or character. Or in my case confidence.
Are you still enjoying or growing?
Hope this helps.