You can request a full 2 years out. You want to be looking when units can be deposited and preferably before most anyone else. While date of request is only a tiebreaker, that can be the difference between success and failure. Some resorts are deposited 18-24 months out, most of the rest are eligible by 12 months. Marriott's tend to be 12-14 months in many cases. Once a given resort is eligible to deposit, the actual units can get to II at any time.
What unit size, area and time of year are you looking for? For example, you'd want to be finalizing your plans now for high demand areas like HI for early 2010. Areas with mostly smaller units and lockoff's (HI, Caribbean) would mean that requiring a 2 BR would dramatically reduce your chances.