If you make him wait (for) more than ten minutes, he'll just walk away.
So I'm a bid confused.
The preposition is optional there. Said that, it depends on the writer's style.
OALD has an entry for it:
I've been waiting (for) 20 minutes.
However, I would not have had this idea, had I not seen that entry some months back. Still, I prefer using the preposition to satisfy myself!
I think its one of those confusing things that doesn't really matter too much. However...
You will wait for a thing (eg 'He waited for the train'), but when it comes to time the common usage is to ignore the for (eg 'I waited 20 minutes', or 'I waited 20 minutes for the train').
But there are times when the for is used, eg 'I was waiting for 20 minutes'
So although its optional, it would not be incorrect to use the for all the time.