I'm confused about sunscreen application?

I was out in the sun today from noon until 6. I applied SPF 30, a healthy slathering. I didn't burn at all but definitely feel the sun from the day. I didnt sweat or swim and I also wore UV glasses. After googling I feel a bit uncomfortable, it is claimed you should reapply every hour. Every hour?!?! That's such a pain and not realistic. Did I get sun damage today even though I applied sun screen???