It depends, if you did it via O2 Gateway then it should be... well, before midnight. If you did it via paper then 48 hours, and if you did it via telephone to O2 from the store, 24 hours.
yeah, ive just ordered it from the carphone warehouse website today. I wanted to know if you can activate it in a few weeks (by 8th August) without incurring a penalty charge or something like that