/(\w{3}) (\d+), (\d{4})(?: (\d+):(\d\d) )?/

##</code><code>##

my @date_parts = split m{[\s:,]+}, $date_string;
if ( @date_parts == 6 ) {
  # date + time
} elsif ( @date_parts == 3 ) {
  # date only
} else {
  die "invalid date/time combo";
}