Very good question. While my therapist's office is pretty strict about the 24hr notice, my psychiatrist is quite lenient. I suppose he would have to be as he himself cancels or rebooks our sessions fairly frequently. He only has limited clinical hours to begin with as his primary focus is his heading up the department and instructing at the medical college of the university. As such, he will get dragged away to meetings, symposiums, etc.

My problem is that I live near 3hrs drive away from my psychiatrist (I would still not give him up for another) and hence must plan the entire day. It does get rather irksome when notice comes late.