You can't choose which type of TWOV you get. Assuming you meet he conditions you get 24h TWOV when your layover is less than 24 hours or 144h TWOV if layover is longer than 24h.
If you have hotel booked, print out booking confirmation and show it when applying TWOV.
when layover is <10h and you're asked about your plans, don't say you want to go to town. Instead explain that you want to go eat landside (cheaper and more choice), have a shower and maybe a short nap in hourly pay lounge (landside arrival level in T3). If you are in Beijing overnight having a hotel booking helps, even if you're not palling to use it.
case 1:
on queue at TWOV counter, nice and friendly lady says 6.5h is very short time to leave the airport, I said I only want to go outside to have a cigarette. She laughed and stamped my passport.
case 2:
On the way back I had actually planned to visit the city, but that plane got flushed with delay, so again my only reason to go out was to have a smoke. To my suprise not a single question was asked or any word at all said to that matter. My face was compared to passport photo, onward boarding pass examined, passport stamped and off I went.