Do I really need to wait 30 minutes for sunscreen to work?

No, the 30-minute rule is mostly a myth. It came from old chemical sunscreens that needed time to absorb; modern mineral sunscreens (zinc oxide, titanium dioxide) protect immediately. The real reason to apply early is to ensure even coverage, not to “activate” it. If you use chemical sunscreen, 10–15 minutes helps it stay put, but thirty is overkill—just put it on before you step outside.