Abby said if you must apply moisturiser first wait at least 15 mins until ultrasun goes on.
For most of us "all day" in the sun would be an absolute maximum of 8 hours, say 10-6.
I used to use Rieman p20 in my 20's It did not stop the UVA, but it was applied to clean, dry skin, wait for 45 minutes and it would give all day protection against burning, and necause the UVA got through you tanned. I was sceptical, but used it for a fortnight in the dominican republic, and the following year a fortnight in the Maldives. It worked both times, no burning, and a tan. Heaven forbid if I knew then what I know now about UVA I would never have done it but I say just to confirm that if it binds to the skin it does prevent burning all day in very hot sun. Ultrasun may be the same, just with UVA included. I also recall it worked after swimming provided you did not rub the skin with a towel afterwards.
It may be that extremely fair skinned people cannot last the full 8 hours, but certainly my fair to medium skin coped with it.