I think the girl is so experienced with hand jobs now, and with what makes guys cum, how quickly they cum etc, that she knows exactly what she's doing. She probably knows how to wank you off better than you do!
In other words she'll pretty well know how to not make you cum within the 5mins, and then with a raging boner any red-blooded bloke who has the money in his pocket will be virtually begging her to finish him off. The only way to avoid that is to purposely arrive with NO MONEY.
And if you do want to avail yourself of this service, and for it to work, you probably need to rock up at hers in some loose jogging pants with no underwear, keeping yourself right on edge until the moment she opens the door. Then as soon as she
takes you in hand you'll spurt forth all over her carpet.
That'll teach her!