Snake mating consists of the male snake penetrating the female snake with one of two hemipenes. The entire mating process between a male and female snake can take a few hours to a few days to complete. This is due to the female constantly trying to slither away from the male, which makes it hard for the male snake to line up their cloacas before the penetration period. Once the female has been penetrated, the duration of the mating process takes around an hour to complete.
The male will stay with the female for two or three days after the breeding. During this time they may mate one or two more times before the male snake leaves the female.
A couple recently caught two sea snakes mating on Bramston Beach in Australia. This was just after they rescued a turtle that was stuck in the mud. You can see a picture of this mating ritual here.