Have you looked at Schedule::Cron? It has good crontab compatibility, and I think that you can rip out the crontab parser relatively easy.

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
[download]

Sean Burke's crontab2english might also have some code which could prove helpful.

#!/usr/bin/perl -w
use strict;

sub cron_parse    {
# This routine takes a time (seconds since epoch) and a crontab entry,
+ and returns
# the next time the process would kick off. Pass the script the last t
+ime a job ran,
# and the cron entry, and compare the result to the current date. This
+ will tell you
# if the job is overdue. The cron entry passed should contain only the
+ 5 schedule
# columns. Day-of-month and Month are ignored (my processes don't use 
+them).

# If anything is wrong with the input, undef is returned.

    my $last = shift || return undef;
    my @last = localtime($last);    # 1 - minutes, 2 - hours, 6 - day 
+of week
    $last = (1440 * $last[6]) + (60 * $last[2]) + $last[1];

    $_ = shift || return undef;
    my @cron_array = split;
    return undef unless $#cron_array == 4;
    my $minutes = &cron_range_populate (59, $cron_array[0]) || return 
+undef;
    my $hours   = &cron_range_populate (23, $cron_array[1]) || return 
+undef;
    my $days    = &cron_range_populate ( 6, $cron_array[4]) || return 
+undef;

    # In theory, I should now have three array references that pass al
+l checks
    for my $day (@$days) { for my $hour (@$hours) { for my $minute (@$
+minutes) {
        if ( (1440 * $day) + (60 * $hour) + $minute >= $last)    {
            return ( "Day $day, Hour $hour, Minute $minute" );
        }
    } } }
    return ( "Day $$days[0], Hour $$hours[0], Minute $$minutes[0]" );
}

sub cron_range_populate    {
    my ($max, $range) = @_;
    my @range = ();
    if ($range eq '*') { return \@{[0..$max]}; }
    elsif ($range !~ /[-,]/) { push @range, $range; }
    else    {
        my @mini = split /,/, $range;
        for (@mini)    {
            return undef if /-.*-/;    # 1 dash per subsection, e.g., 
+"2-6-9, 24" is invalid
            if ( !/-/ )    { push @range, $_; }
            else    {
                return undef unless /(\d+)-(\d+)/;
                return undef unless $1 < $2;
                push @range, ($1..$2);
            }
        }
    }
    return undef if $#range == -1;
    for (@range) { return undef unless ($_ >= 0 && $_ <= $max); }
    return \@range;
}

my $next_job = &cron_parse(time, '04 13-16 * * 01,02,03,04,05') || "ba
+d input";
print "Next job kicks off : $next_job\n";
[download]

Comments welcome.