Well the meetings are heavily cut, I remember reading that typically each of the pitches is atleast a couple of hours. The sharks have no information on the companies pitching before they walk in to the room, but I'm sure the producers do some home work to only let in entrepreneurs that will make for good TV. The sharks are all smart people so they know what to ask but its no where near a ten minute affair.

All the due diligence is done after the show ends. The deal you see on TV is only tentative until after the due diligence. Quite a few of the deals on the show have actually fallen through after some shady things have been uncovered