This is quite the risk, you should settle to play wherein you'll have instant withdrawals and probably just really fast actions, its not secured if you'll have to wait before you get the payments, but if the casino that you are playing is legitimate and you really trust it then I don't think that you are taking the risk, just play safe and always know what sites to trust.
You cannot assume that instant payment based casinos are legit and delayed payment based casinos are not legit.
As far as I am concerned, I will not bother about delayed payment nor instant payment but my casino should keep their words.
It means they should process my withdraw request as per their terms and not based on my case. If they are having any general term for how much time they will take for processing withdraw then I will not be having any problem with them to continue. Practices should be in general and not should be a special case for winners alone.
In the past I had faced a situation of my withdraw request put into "under investigation" status. Then I have contacted their customer care and they replied it will be processed in 24hrs then I got my money. But, I never went back to them as they have not informed me anything about investigations on my request well in advance I am sure that I have checked thoroughly their terms and conditions before start playing with them.