As @TheMonkWithoutVows pointed out in Re^2: Sheer idle curiousity . . ., the code

$wait = 0 unless abs($wait);
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unlike other examples, never assigns anything to $wait if $wait is -34.

Proof:

my $wait = -34;
$wait = 0 unless abs($wait);
print $wait;
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prints -34

So if you change your benchmark to

$wait = 0 if abs($wait);
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you'll see, difference is small (I got 4%). (even through abs() is still used).

UPD:Oh, @TheMonkWithoutVows and you(OP) are same persons :)