>>> datetime.fromtimestamp(time.time() + (1800000 - (time.time() % 1800000)))
datetime.datetime(2011, 12, 4, 13, 0)
>>> datetime.fromtimestamp(time.time() + (1800000 - (time.time() % 1800000)))
datetime.datetime(2011, 12, 4, 12, 59, 59, 999999)
>>> datetime.fromtimestamp(time.time() + (1800000 - (time.time() % 1800000)))
datetime.datetime(2011, 12, 4, 13, 0)
>>> datetime.fromtimestamp(time.time() + (1800000 - (time.time() % 1800000)))
datetime.datetime(2011, 12, 4, 12, 59, 59, 999999)