use Time::Local;
 
$start = '2013-10-28T18:59:52.863Z'; 
@parts = $start =~ /^(.{4})-(.{2})-(.{2})T(.{2}):(.{2}):(.{2})\.(.{3})Z$/;
$start_secs = pop(@parts) / 1000;
$start_secs += timegm reverse @parts;
print "start_secs : $start_secs\n";
 
$end=timegm(gmtime());
print "end_secs : $end_secs\n"; 
$diff = $end_secs - $start_secs;
 
print "$diff";