I started wearing sunscreen on my face every day (which I wish I had started doing way sooner) to help prevent damage and wrinkles. Do I have to reapply every day for it to work while I'm out and about? Or does applying it today mean it'll still work tomorrow as long as I'm only in the sun a few minutes at a time? And why?

I understand it's like a barrier that UV rays can eventually break through, but how long does the barrier stick around?