What's a reasonable amount of time to wait for a telehealth call?

I was supposed to have a telehealth meeting with a specialist today to review some MRI's I got done almost a month ago.

I've seen this doctor twice and they're always on time or early.

My meeting was supposed to start at 3:30 but they requested I join 15 mins early to fill out some online paperwork. It's been over an hour now that I've been waiting with no communication from their office. I just looked and they're closed on mondays and not answering the phone but my confirmation email clearly says today (9/26) at 3:30.

I have a lot I need to do as I'm leaving town for a week in a few days, and can't spend my whole afternoon waiting for this appointment. I also have to pee but I'm scared to step away from my computer lol. What's a reasonable amount of time to wait for a doctor before giving up?