You will receive a invitation, don‘t book anything until you receive one. He could fail, the course could be held, if they fail too many or to many people quit. In the old days people failed the very last day (Graduation Day), I had 3, get dress to graduate and be told they failed. This was when Basic training was 15 weeks. You never know until the last week, so you took your chances having family come. If you were close to failing. You will get about 3 weeks give or take.
As for post training, what trade is he? He may go go as soon as he is done. or wait for more soldiers to graduate to fill the next course. Some courses graduate,spend a day with family, then head out for DP1 (trade training). There is no OJT for any trade, only for people that transfer from one trade to another (LOTP). But they are Snr Corprals with time in. There is two courses of Armour ( tank/Recce crewman) waiting for training in Gagetown. Some have been there for months, in a holding Troop.
If he would have graduated just before Christmas, he would may have went home for Christmas leave. If you E-Mail me I can give more info or I could give my phone and discuss it.