I think 48 hours isn't enough. It'll cause conflict with the timeframe of giveaways and contests, obtaining the graphics for the group or award, and with the timeframe the artists of the userbar and the award icon will get. I think two weeks more or less is fair amount of time.
I think it is plenty of time, members should purchase things after contests are complete not before, also userbars should be made prior to purchasing as well.