And those of us hired around when the Merger was announced have been on reserve a little over 2 years. (And we're very happy you're here!)
How long on reserve also depends on what base/AC you're in - how big and how senior. In a relatively small (and junior) category like one of the DC9 cats, there may only be 15 reserves - so you don't have to have as many bodies under you to hold a line. On the ATL M88, there are over 500 pilots in the category, so about 100 of them are reserves. Add in the seniority factor, and I've heard it takes about a year of pretty good hirring to hold a line there.