You pay in advance. To be honest, I'm not sure if they write down the time as you leave the counter to go into the range or once you get in there. If I had to guess, it's when you leave the counter because I doubt the watch you go in there first before writing down the time.
They keep your license, so I'm sure they'd make you pay for any extra time before giving it back.
They keep your license, so I'm sure they'd make you pay for any extra time before giving it back.

