I think they have to stay a minimum of 18 months prior to being recalled and no more than 5 can return per month. To be honest, I don't know why anyone would do this...they will have to sit reserve for at the very least 6 months (Pinnacle reserve...not NW reserve, I'm talking 18-20 days of airport ready reserve/ month). Plus, with the number of First Officers that have the time to upgrade now, there is almost zero chance that they would upgrade in the next 18 months. I would take a job at Home Depot and enjoy life with friends/family for 18 months and wait for the recall before being subjected to our crew scheduling/planning practices and only seeing your family 10 days a month! Life is too short!