my $t1 = "05:07:53.249";
my $t2 = "05:07:55.401";
print to_milli($t2) - to_milli($t1);

sub to_milli {
	my @components = split /[:\.]/, shift;
	return (($components[0] * 60 + $components[1]) * 60 + $components[2]) * 1000 + $components[3];
}