If you have a choice about how the date/times are represented, using 24 UTC time in this format will allow you to just do a simple alpha sort on the date/time field. The leading zeroes are important.

#year-month-day with leading zero'es!
2010-08-06 13:12:13 # "Aug 6th, 2010 13:12:13" (1 pm+)
2010-01-01 21:01:03 # "Jan 1, 2010 21:01:03" (9 pm+)