Does California's final paycheck penalty run for the full 30 days even if I'm paid on day 5?

No, and this is a common point of confusion. The penalty accrues one day at a time, and it stops accumulating the moment you're actually paid in full. Being paid five days late means you're owed five days of penalty wages, not the full 30-day maximum.

The 30-day figure represents a ceiling on how large the penalty can grow, not something you're automatically entitled to regardless of how quickly you were eventually paid. Any source suggesting you're owed the full 30 days no matter what is overstating what the law actually provides.