I haven't done an rb for a while but I used to quite regularly. I used to put them up as much as three or four weeks ahead of the date and get an initial flurry of bids, then very little for a while, then another burst as the date got close. I never let it go right to the wire so possibly missed some last minute bargains, but I like to have everything sorted at least 2 or 3 days before the event. Depends what suits you best. I think rbs are ideal for outcalls as you get bids from the part timers who can be fun and enthusiastic. But whenever I've booked a room for an outcall in the last 12 months its always been to see someone I've seen before, hence my not doing an rb for a while.