My understanding of these parking stall systems is that they often include bundled handheld devices for parking attendants. These handhelds are used to issue tickets and include a nifty feature of alerting the attendant when a particular stall number runs out of time. It is, of course, then up to the attendant to venture to that space and verify that a violator's vehicle remains parked. If they are not on lunch and promptly make such a verification you will most certainly end up with a ticket. This happened to several friends, all of whom were issued tickets two to three minutes after their prepaid time expired. If the attendant is on a lunch break or if there is not a high parking turnover in your lot you might get lucky and be overlooked. Bottom line: it's a risk you are free to take.