I think the -- flag to stop option parsing is only necessary if something you want treated as an argument actually looks like it might be an option, e.g. -999 or --foo. In the code given it is not required but it does no harm and using it is not a bad habit to get into.

$ perl -MPOSIX -le 'print mktime @ARGV' -- 56 34 12 4 1 115
1423053296
$ perl -MPOSIX -le 'print mktime @ARGV' 56 34 12 4 1 115
1423053296
$
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I hope this is of interest.