I said 30 minutes because I *have* waited 30 minutes for ex-marriage counselor before (he was habitually late, though usually not that late). But in that case, he had a receptionist who confirmed he was there and let him know his next client was there.

My current T is extremely prompt (he's been 5 minutes late at the most, usually exactly on time), so if he's more than 5 minutes late, I assume either he messed up something with the scheduling or that something is wrong. So I'd text him. Then if I didn't hear anything back in 5 minutes, I'd try texting again. After 15 minutes, a phone call, then if nothing, I'd be more likely to just leave, maybe wait until 20 minutes because it is so unusual. He doesn't have a receptionist, so I'd have no way of knowing if he's in the office, is back with another client, etc.