Erm, given start and end as time_t values (use Date::Parse or whatever to get them there) just convert your interval into seconds and add.

sub intervals {
  my( $start, $end, $interval ) = @_;

  my @ret;
  my $cur = $start;
  while( $cur <= $end ) {
    push @ret, $cur;
    $cur += $interval;
  }
  return @ret
}
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There is bound to be something useful in the DateTime module set. But you can also implement this yourself with some judicious use of gmtime() and Time::Local.

As an aside, you might be interested in the Reefknot project.

I can't test this right now, but I hope it will give you a start:

use strict;
use DateTime::Span;
use DateTime::Event::Recurrence;

my $set1 = DateTime::Event::Recurrence->minutely( interval => 30 );

my $date1 = DateTime->new( year => 2002, month => 3, day => 11 );
my $date2 = DateTime->new( year => 2003, month => 3, day => 12 );

my $set2 = DateTime::Span->from_datetimes( 
             start => $date1, 
             end =>   $date2 );

my @dt = $set1->intersection( $set2 );

for ( @dt ) {
    print $_->datetime, "\n";
}
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