Does the dial alarm/timer work for this watch? Can I set up an alarm or timer?

The other answers are confusing. There is no alarm. The rotating bezel simply helps calculate elapsed time by marking the start of some period, showing roughly how many minutes have passed since that time. The idea was that divers stop for decompression at certain depths for certain periods ascending after a dive. After strenuous activity breathing dense gas mixtures brains are not optimally operational so analog dive watches helped remember the beginning and calculate the end of decompression stops. This simulation helps you remember when your parking meter needs feeding.

does it have a back light?

No backlight. Meager phosphorescent paint on hands (just a dot on second hand); nominal, useless paint on numerals. If you want to check the time immediately after going from full sun into a dark theatre or cave the glow is plenty—otherwise you'll want a torch. (Or you'll reach for your 'phone to use its light and realize it can tell you the time just as well.) This isn't meant to disparage; backlight burns battery power and small hands can't hold much paint, so a small watch with a small battery can beneficially dispense with internal illumination.

Have you worn this watch snorkeling more than once?

Yes, many times. This is the only watch I've owned unobtrusive enough to leave on all the time. I never take it off, skin diving included. I rarely descend below 3-4 meters; that's well within its pressure range.