I use the hand trick with the sun.

4 fingers between the sun and the horizon is about an hour. From time to time, I just take a measurement.

For every 4 fingers of additional height until noon is an hour, from every 4 fingers of less height after noon is an hour.

Edit: One of the best times to check if when you’re at the top of a water slide tower, since they usually give you a nice view of the horizon.

Not to be that guy, but why don’t you want to wear a watch? This is like one of the prime use cases for a waterproof wrist watch

I think this might be what you want: https://www.amazon.com/Waterproof-Stopwatch-ANTEQI-Function-Calendar/dp/B0BZGTDSRT/ref=sr_1_6?crid=2KEZXYCGFMX2S&keywords=waterproof+timer&qid=1687566752&sprefix=1tb+micro%2Caps%2C254&sr=8-6

But if you search amazon for “waterproof timer”, there are other options.

Maybe every other ride? I just feel it out, does it feel like an hour? Then sun cream. It’s not like putting it on too often is an issue.

Make sure it’s waterproof though. If not then you need to reapply after every time you go in the water.

Doesn’t the water park have clocks visible? You could use those.

If you have a closeable pocket in your swimpants then take a small tool and take your watch off its wrist straps. Put that in the pocket and you will be able to check the time whenever you want.

Yeah, it really annoys me that at the water park I usually go to (not the best, but the closest one to me) there aren’t any clocks around, even in the food stalls or places like that. Fortunately, when I look around I can usually find someone wearing a watch or looking at a phone that I can ask.

There’s a few bands and stickers that react to the amount of uv exposure

https://intellego-technologies.com/smartsun-bands/#:~:text=Intellego’s SmartSun Bands are designed,the course of the day.