I agree that 10min is a threshold. We have a bus line nearby that has a 15min interval. It's close to useless for short trips, and I only use it rarely.

The busses with 10min interval are okay. The average wait is still longer than I'd like, but it's not quite as frustrating.

But a 5 minute interval should absolutely be the goal. It's probably not possible for many bus lines because of traffic, but for rail and tram lines its not a problem.

With a 5 minute interval public transport becomes more appealing than driving.

One reason why wait time is so important is that people often need to change lines. If you want to take two busses with a ten minute interval, you have to leave 20min early to make sure you get there on time. That makes driving a lot more attractive...