The updated solution still has a problem, IMO, with that pesky  \W anchoring the start of the match. Is the following really what you intend?

>perl -wMstrict -le
"my $input = '12:00am, 5:00pm,8:30AM';
 while ($input =~ m/\W([1-9]|[01][0-2]|2[0-3]):[0-5][0-9][ap]m/gsi)
 {
         print qq{This is a valid time!\t$&};
 }
"
This is a valid time!    5:00pm
This is a valid time!   ,8:30AM
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