An incorrect number of arguments is a very different error than an incorrectly formatted option. Report it separately.

use strict;
use warnings;
# More Realistic values are required for these constants.
my $VALID_DATE_FORMAT = qr{\d\d/\d\d/\d\d\d\d};
my $MAX_DEVICE_NUMBER = 17;

if (!@ARGV or @ARGV>2){
    die "Usage:...\n";
}

my ($device, $date) = @ARGV;
$device =~ s/\s//g;
$date //= q();

if ($device =~ m/\D/ or $device < 0  or  $device > $MAX_DEVICE_NUMBER)
+{
    warn "Invalid device number - Must be an integer < $MAX_DEVICE_NUM
+BER\n";
}
if ($date and $date !~ /$VALID_DATE_FORMAT/) {
    warn "Invalid date - Must be mm/dd/yyyy\n";
}
print "device: $device\ndate: $date\n";
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