3.4.3. Discussion

Calculating with Epoch seconds is easiest, disregarding the effort to get dates and times into and out of Epoch seconds. This code shows how to calculate an offset (55 days, 2 hours, 17 minutes, and 5 seconds, in this case) from a given base date and time:

$birthtime = 96176750;                  # 18/Jan/1973, 3:45:50 am
$interval = 5 +                         # 5 seconds
            17 * 60 +                   # 17 minutes
            2  * 60 * 60 +              # 2 hours
            55 * 60 * 60 * 24;          # and 55 days
$then = $birthtime + $interval;
print "Then is ", scalar(localtime($then)), "\n";
Then is Wed Mar 14 06:02:55 1973

We could have used Date::Calc's Add_Delta_DHMS function and avoided the conversion to and from Epoch seconds:

use Date::Calc qw(Add_Delta_DHMS);
($year, $month, $day, $hh, $mm, $ss) = Add_Delta_DHMS(
    1973, 1, 18, 3, 45, 50, # 18/Jan/1973, 3:45:50 am
             55, 2, 17, 5); # 55 days, 2 hrs, 17 min, 5 sec
print "To be precise: $hh:$mm:$ss, $month/$day/$year\n";
To be precise: 6:2:55, 3/14/1973

As usual, we need to know the range of values the function expects. Add_Delta_DHMS takes a full year value—that is, one that hasn't had 1900 subtracted from it. The month value for January is 1, not 0. Date::Calc's Add_Delta_Days function expects the same kind of values:

use Date::Calc qw(Add_Delta_Days);
($year, $month, $day) = Add_Delta_Days(1973, 1, 18, 55);
print "Nat was 55 days old on: $month/$day/$year\n";
Nat was 55 days old on: 3/14/1973

3.4.4. See Also

The documentation for the CPAN module Date::Calc