my $db;  # local connection used to retrieve time
$db =  ... however you choose to connect a handle

=item timestamp($timestring [, $future_flag])

=cut

  sub timestamp {
    my($time,$future) = @_;
    local($db->{RaiseError}) = 0;
    local($db->{PrintError}) = 0;

    # Timestamp could be absolute.
    my $val =
      scalar $db->selectrow_array(q!SELECT EXTRACT('EPOCH' FROM TIMESTAMP ?)!,
				  undef, $time);
    if (defined $val) {
      $db->commit;
      return $val;
    }

    # Well, it's not, so let's try it again as a delta from today.
    $db->rollback;
    $val =
      scalar $db->selectrow_array(q!
	SELECT EXTRACT('EPOCH' FROM (TIMESTAMP 'now' + INTERVAL ?))!,
				 {
				 }, $time);
    return $val unless !defined($val) or (($val >= time) and !$future);

    # Hmm, that gave us nothing, or a time in the future, and the caller
    # didn't want that.  Try one more time, using a subtraction on the
    # delta.

    $db->rollback;
    $val =
      scalar $db->selectrow_array(q!
	SELECT EXTRACT('EPOCH' FROM (TIMESTAMP 'now' - INTERVAL ?))!,
				 {

				 }, $time);
    return $val;
  }