My husband has been sent to rehab for a 28 day program but his probation is over 14 days before the program is can he leave when probation is over

It depends.  Probation is extended when there is a violation.  If he is going because of a violation or in order to avoid a violation he shouldnt check himself out.  Importantly, why would he??  The probation officer wouldnt send him to rehab to harass him, he may have a drug problem.  May be he needs rehab.