It would be good to mention here that all quantities of nutrition and hydration are based on elapsed time, not saddle time. That's a very important distinction.

Some folks on here don't understand the basics behind the recommendations by scientists, which not incidentally, the Army agrees with. An army doesn't fight well with incapacitated soldiers. Some don't seem to believe it, but the Army recs are about right for soldiers being reliably able to do what they do, that's all soldiers. They're not all endurance athletes, though not bad either. The Army (and I) are saying that there are limits on human performance. There is no protocol for doing continuous hard aerobic exercise at over 100°F for many hours. Don't do that. I don't have one, the US Army doesn't have one. You'd have noticed if you'd read the link. It's real simple. You can die. You have no idea whether your risk from hydration was worse than your risk of hyponatremia unless you gave someone a blood sample to analyse. You should have read that ncbi link more closely.

My advice is pretty clear and based on 20 years of experience riding in hot weather. Not as hot at 110, only some hot multi-hour pass climbs, long rides in Eastern Washington in July and that sort of thing, but plenty enough so that I figured out what to do and what not to do. Actually, I didn't "figure it out". I read the Hammer, Ultracycycling, and other scientific advice and learned how to implement it.

I'll make it simple for everyone.

Do not: drink more than 1 liter per hour, 1.2 liters is the limit, that's 40 fluid ounces.

Do not: ride more than 3 hours without peeing. If you have to, stop somewhere with water and shade and drink until you pee. I realize that some find this ridiculous, but this is how you stay safe. Disregard at your own peril. There is no other reliable, in-the-field method of determining hydration state. The skinfold test only shows dehydration. Color of said pee doesn't matter.

Do not: stop drinking because your water got warm.

Do: take enough electrolytes of your choice that you are thirsty enough to want to drink that much water. Never force water. If you aren't thirsty but you should be, more electrolytes, stat. You'd know if you were drinking too much, because you'd have to pee more often than every 3 hours. If you like pretzels, fine. I like Endurolytes because I know what's in them.

Do: watch your heart rate. If it climbs more than ~20 beats over what it should be for that effort, you need shade and rest. Plan for that in advance. Know where your shade and water will be. Always have a ride plan in hot weather. Look at your distance and therefore time between water stops and have enough water on board, plus a little.

Do: wear skin-tight technical clothing and only one layer.

Do: watch your forearms. If they go dry, you need to find shade and water stat, realistically within 1/2 hour. If that's too far to ride, you need to hitch. If you wear sunsleeves like I do now, watch your sweating from other areas. You must be sweating the entire time. If you've followed the above advice, that won't be a problem.

There's a good discussion of heat adaptation strategies here: https://www.tandfonline.com/doi/full...0.2019.1666624
Short form: For adaptation, one needs to ride some in the heat almost every day.

My wife and I did the one-day 200+ mile STP, on our tandem at a team age of 139 and we never were a strong team. The weather was the hottest ever recorded for this ride. We took 15.5 hours to do it. In the first 100 miles, riders were passing us. In the second 100, we were the ones doing the passing, simply because we followed the above advice. At the finish, we were the first to board the first bus to Seattle. It took ~1.5 hours for the bus to fill, not at all my experience on cooler days. Our time was really slow, but not as slow as most folks because we kept our average speed about the same all the way. And, well, I admit that we only stopped 4 times, so we did go a little over 3 hours between pee stops. Over the long run, you're faster if you take care of yourself, have enough food and water, and are able to stay on the bike.