Lil Wayne schedules prison time

It's yet to be convincingly explained to me how Americans get given prison dates the way the British get hospital appointments - an invitation to come over some time in the future.

Lil Wayne, American justice has decided, must spend time in prison to make society safer (he was waggling a gun round.)

Fair enough. But if prison is vital in turning him from a gun-toting threat to society into a good and honest man, why does he not have to go until February? Isn't it a bit dangerous having him wandering round over Christmas, potentially shooting at Santa as he flies overhead?

Or... are the authorities really saying that prison has such little effect, it doesn't really matter when you go?