change

while ($time_val == "08:28:00") {
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to

if ($time_val eq "08:28:00") {
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Update: (thanks to Perlbotics)

also change

$time_val="$hour:$min:$sec";
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to

$time_val=sprintf("%02d:%02d:%02d", $hour, $min ,$sec);
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Then all values smaller than 10 will be formatted with two digits.