As a guy, being in a situation/location/environment where asking out a girl is not appropriate, and so having left her your own phone number...
How long is it safe to say she's not interested or changed her mind? A few days or a few weeks?
There's no point in wasting your time wondering about that. Just continue your efforts to seduce her, regardless of if she calls you or not. Use your brains, that way is for sure not the only one. Finding these ways is what you should waste your time with.
Name me a situation where asking a girl out is inappropriate.
Girls generally like a guy to take charge, if you are waiting for her to call you, don't hold your breath.
> a situation where asking a girl out is inappropriate
Don't worry about the call, unless she seems harebrained. Then, I recommend asking her if she forgot or lost the number. I mean, that sounds like me.... so yeah.... x3
I'd say a few days. But don't give up, just continue seducing (but nothing to obvious xD)