I'm not sure if this has already been posted before, I have looked using the search but no matching results.
When waiting for the shops to re-stock items which takes 2 days, the process can be very slow and tedious :S watching that little marker count down the hours.
To make life easier try this:
Set the wait time (usually 24 hrs) then press A to begin countdown and immedietly press your Xbox Guide button and you will hear the tick sounds in the background rapidly counting doen at about 3 per second instead of the usual 1 every 1.5 second. I know this isnt a huge improvement but when you waiting for that special something to appear in the shops, the amount of time you save waiting is huge!!
Try it and hope it helps.
Nibbz
-Just to confirm, this takes the total wait time (real time) from 56 seconds down to 12 seconds when passing a total of 48 hours game time-