I know that typically they recommend to apply chemical sunscreens about half an hour before exposure.
How about non-chemical sunscreens, in particular with titanium dioxide only?
Being a physical reflector I would guess that it does not require to be applied with any advance, just enough that it is on the skin from the moment you expose to the sun.
Is this correct or there needs to be some delay between the sunscreen application and the sun exposure?
Thanks!

The mineral sunblocks will work instantly after application.

Many thanks Dr. Pickart.