The first thing he must understand is that the extra-board is NOT a bid.
There are two call blocks for extra-board, 5am-9am and 5pm-9pm...this is when a majority of our extra runs are called out. Everyone is required to sign a call block waiver stating whether or not they want to be called outside of the call block. If he signs the waiver saying "do NOT call" outside of the call block, then a junior driver who signed "do call" can be offered a run outside of the call block ahead of him (which shouldn't be an issue if he's the new guy). The drawback to signing "do call" is that they can/will call whenever a run is available...at all times. When a run is called, you're allowed 1.5 hrs to show and 30 mins to gate for a total of two hours to gate from the time called. This usually isn't a problem unless you actually live an hour and a half away.
As for when he'll run depends on his location...if at an EOL center it will almost certainly be PM, if at a hub it varies. Satur"day's" are optional (volunteer) although if on the PM, he'll work Fri night-Sat morn, then he won't be available for Satur"days". As for "if he'll get to work", again, that depends on his location. Right now shouldn't be an issue but things do slow down in the winter.
Hope this info helps and good luck.