Wee. I decided to try it out myself.
time.gmtime() will convert the seconds since epoch to a date. So if we take the current seconds since epoch time.time() and offset it back a day, voila!
import time
def time_zone( offset = 0 ): # DEFAULT = GMT
new = time.gmtime( time.time() + offset*60*60 )
return "Day: %s | Month: %s | Year: %s\n%s:%s:%s"%(new[2],new[1],new[0],new[3],new[4],new[5])
print time_zone( -5 )
I'm -5 from GMT, so if I then set it to -29, it gives me yesterday's date.
Hope this helps. =D