Plenty of young FOs have been taking GLC FO bids while still on probation. Personally, I think they are OUT OF THEIR MINDS. I get that they want the international and larger aircraft experience before seat-locking themselves with their first upgrade to PIC. But they have no retreat rights while on probation. And there have been a fair number of failures/terminations of probies. Nobody thinks it can happen to them but ANYBODY can have a bad day, run into an evaluator with a chip on the shoulder, whatever. Be smart and wait a few more months.

JMHO