The last 5 or 6 reservations appeared online < 2 seconds. They were on spg.com before I received an e~mail from spg's reservations system. I often switch from one property to another when my corporate rate becomes available, so I wait for the reservation agent to confirm the new reservation prior to cancelling the other. Once they say it is confirmed, I cancel the original rez, about the same time they say, "Hey, CaptainG, did you know you have a reservation at this other property in the same city."
By the time I tell them to look again, they see it as cancelled, and their new reservation appears on spg.com This is with paid rates (not pre-paid and not award stays). Award stays take some time (I assume starbase has to query the point balance of the member and to save processor load on the CPU, they don't update as often). Pre-paid rates often take a few hours to show up correctly, and sometimes when they do show up immediately, they will show a different rate and different room-type for half-a-day until starbase query's the master room availability list (wherever that is held) and synchronizes with that).