Does this do what you need? If so, I'm guessing it should do a bit less work than DateTime would..

my ( $minute, $hour, $day, $month, $year, $wday ) =
          ( localtime( $start ) )[ 1, 2, 3, 4, 5, 6 ];
next unless (($wday >= 1) && ($wday <= 5)
            && ($hour >= 8) && ($hour < 18));
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