Last prac day i went to had about 5 sessions of about 6-7 laps, it just depends if there are things like oil spills on the track etc etc.
You dont have to do every lap of the session, if your car overheats you can pull into the pits or drive a bit slower just dont get in the way of other cars. When i come into the pits i do a few very slow laps of the pits to help the car cool and dont hold with your foot on the brake's while they are hot.
Overtaking is allowed on the straights, but is not permitted under brakes.
I recommend that you have new brake pads or near new, as last prac day i had to drive home with no rear pads left and take a tyre pressure gauge as you will need to adjust the pressure when the tyre's are hot. Pressures will jump about 4-6 psi or more.