I need to store a timestamp in an XML file, read it in, compare it to another time, and then store it back in the XML file. (I read in two timestamps at a time, and need to check if the intervals overlap).

So, how can I take a timestamp, such as Jan 05 21:30 and convert it to GMT (milliseconds since the epoch?), compare, and then convert that timestamp back to milliseconds?

Any help is much appreciated,
Thanks!