Probation at AA is 12 months or 400 hours and a training event (R9). Typically by second year pay, as an O-4, you're losing money doing mil. Third year pay isn't even close.
With the movement and pay the way it is these days, I can't see why anyone would drop long term mil leave after the first year unless you live at your ARC unit and are commuting to your airline gig and just want to stay home/not care about the pay.