We sent out our Save-the-Dates as soon as we booked a wedding date and hotel location (about a year in advance). We're planning to send out invitations about 6 months before our wedding, and will ask our guests to RSVP 4 months prior to the wedding. With 4 months, this will give us time to finalize reception costs, favors, OOT bags etc. But if your rooms have to be booked by January, perhaps you should send out formal invitations by September 1st and ask for RSVPs by November 1st (which will give you a 1-month cushion in case you have to track down guests who don't respond -- which will probably happen, unfortunately!