I've had really mixed experiences with the time estimates in London. Sometimes it will specifically say that a train/bus will arrive at 17:00, 17:10, 17:20 etc, but sometimes it will just say "every 10 minutes". I haven't worked out the reason for it, I've seen both versions on exactly the same services before.

That's pretty much my only complaint about an otherwise perfect app though, but you're right that those little errors can add up to be quite inconvenient over a long or rushed journey.