Well, run it and see if $dateTime is set to what you expect. On my system, it's set to 16, which is probably not what you expect. The comma seperates arguments to a function, or if not used in a function call, executes all of the statements listed. In this case, it's first executing:

my $dateTime = $hour
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then

":"
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then

$min
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Neither : nor $min will do anything, so Perl complains this probably isn't what you wanted.

Probably you meant to use the dot operator (.) to concatenate these together as strings, or else use the strings as arguments to join.