Pre-empting iNetBet's response (er..not sure they have access to this forum Bryan?), from my research there appears to be a fundamental difference between how RTG, Playtech and Microgaming flush cashouts within the software. This is how I understand it though it's based on what I have been told, not first-hand experience of the back-end software.
Microgaming software allows casinos to set the "reverse time" (pending withdrawal) for any individual player, in the latest release the pending period can even be removed altogether I believe. Most casinos set a default time for all players ranging from 4 hours, the lowest default I have found, to 48 hours, the largest I have come across. Once this period is reached, each cashout is queued for payments and the casino usually processes them once a day on the following day, although many don't do weekends. The software also allows the casino to set a different pending time for different days of the week, so that for example, they could choose to give you 12 hours on weekdays, but return to 48 hours at weekends on the basis that their accounts department don't work weekends. Some do this, though the majority have one setting.
With Playtech, the software only allows a general setting which covers all players. By default, this used to be 5 days. A casino could choose to reset this to a lower period, but not on a player-by-player basis - everyone gets the same - unless this has changed recently. Similarly to MG casinos, the cashouts are then queued for processing by the casino at a time they choose.
With RTG however, the software leaves it entirely up to the casino. From what I gather, the cashouts sit in the "reverse pending" period ad-infinitum until the casino chooses to process them. In iNetBet's case this is often twice a day, with Club World it is at least once a day. But essentially it is entirely down to the casino to remove the cashout from pending and process the cashout.