Being on the other side of the fence here, I can say that it’s false, at least for us.
I had a webmaster that registered a few weeks ago, and got the largest single comission we sent out in a while, roughly $900 for one week net.
So from what I see, time has nothing to do with performance or how much you will be paid..
From my previous work experience, I never worked so closely with webmasters to say if I could detect a similar pattern as stated above by the prof.
Personally, I am a strong advocate of giving just reward when due. I mean, what’s the point of promoting when you can’t see the result and be paid for them?
That’s just my $0.02 worth.