Any time that you feel like you want to cut your losses is fine. There is no guideline.
I've wasted my time waiting 15+ minutes after arriving and never heard back from the provider.
Once you get the feeling that you're being ignored, it's probably a good idea to leave.
It's a difficult call to make because you're in a heightened state of stress and excitement, but you need to take control of yourself and the situation.
The only justification you need is that you're feeling uncomfortable with the way the arrangement is progressing.