In my personal opinion, the SPF works great only as long as you RE APPLY. I have gotten burned very badly by only applying once or twice in one day. You need to stay on top of it and apply as needed as often as needed. If you are light skinned I would reapply once an hour or every 45 minutes. If you are darker every two hours should be sufficient.
Anytime I go away I use this not only as a SPF Sunscreen but to keep my skin hydrated. It works very well, especially when I traveled to Mexico and DR it last me pretty much all day. When I went swimming, that was the only time I reapplied.