How do I find difference between two timestamps?

my_perl has asked for the wisdom of the Perl Monks concerning the following question:

Hi,
I have 2 timestamps in following format

$start = 2004-11-15T18:59:52.863Z

$end = 2004-11-15T19:09:52.972Z
[download]

I need to find how many hr, min, sec, millisec is between them
Please help
Thanks

20041116 Edit by ysth: code tags