In theory 50 weeks out, same as paid stays. HOWEVER... not all hotels post their inventory then.

For example JW Marriott Orlando doesn't post paid or stay availability until about 36-40 weeks out.

Vail Marriott doesn't have any award availability posted for mid-December through January yet. Paid stays for mid-December through January just showed up yesterday morning.

I would start looking on Sunday April 20 and/or Monday April 21, and then check daily, or at least weekly, thereafter.

Note if this is a high demand property, especially for conferences then that is one reason for the delay in hotels posting their availability. While I don't think this is right, it happens and those from, or associated with, Marriott may well say otherwise. In that case I refer you to this thread for more info: Marriott Concierge - lack of inventory availability