Time::Piece is cool.....

#!/usr/bin/perl -wT
use strict;
use Time::Piece;

my $time    = "10:30:05";
my $delta   = 1000;
my $newtime = deltatime($time,$delta);

print "$time + $delta => $newtime\n";

sub deltatime {
  my $t = Time::Piece->strptime(shift,"%T") + shift;
  return $t->strftime("%T");
}
[download]

Or, as a one liner....

perl -MTime::Piece -le'print+(Time::Piece->strptime(pop,"%T")+pop)->st
+rftime("%T")' 1000 10:30:05
[download]

-Blake