DRY = Don't repeat yourself

Symbolic references are just implicit hash lookups, doing them explicitly is better in the vast majority of cases.

The for-solution you showed is aliasing which has similarities to referencing, but should not be confused.

Update

> Now $_ = zeropad($_) for $sec, $min, $hour, $day, $month;

> OTOH? That's what I'm talking about!

No you weren't.

But FWIW, aliasing it's also feasible with hash values.

Consider

$_ = zeropad($_) for values %time

and revaluate the clarity of concise code.