The result of timelocal will depend on the local time zone. For example, when I ran your code it printed 18123 because I'm at GMT-0500. Of course, that can be avoided by using gmtime insead. The following code prints the expected 3723:

use Time::Local;
my ($hours, $minutes, $seconds) = (1, 2, 3); #insert your regex here
print timegm($seconds, $minutes, $hours, 1, 0, 70);
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Unfortunately, even that's not a complete solution, because the epoch is not Jan 1, 1970 on all platforms. On the Macintosh, for example, it's Jan 1, 1904, and the output is 2082830523.

There's still a way to do it with timelocal, though:

use Time::Local;
my ($hours, $minutes, $seconds) = (1, 2, 3); #insert your regex here
print timelocal($seconds, $minutes, $hours, 1, 0, 100)
      - timelocal(0, 0, 0, 1, 0, 100);
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The choice of year is relatively arbitrary, but note that you mustn't pick a time of year that will be affected by daylight savings.

So, you can solve this problem using Time::Local, you just have to be careful about how you do it.