dont want to offend anyone but i find this thread really odd!
never needed more than half an hour with the dealer to decide on a car. get in, drive along a fast A road/dual carriageway, drive slowly around a town, then give it an absolutely thrashing down a country road. keep an eye on the fuel guage (shouldn't move much if at all). if i'm honest i'd get bored driving a car alone for more than half an hour or so if i didnt have anywhere to specifically get to, you can get a real feel for a car without spending hours behind the wheel.