There’s quite a bit of individual variation in hydration need, as our sweat rates vary by 10x across the population, and some of that variation carries into your rest state, too. You’re always sweating, to some small degree, and dehydrating through breathing. Sleep time is 8-10 hours of dehydration.
I push water and decaf until I can notice the bladder really starting to turn it over - having to hit the head every 30-60 mins. That let’s me know “I’m there”, then I just back off to thirst / desire. I embrace high sodium food, too, as I’m “charging up”.
I’ve noticed the amount of water I need early in the day ties in very closely with the weather. In dead of winter, drinking to thirst works fine. In summer, that’s a straight path to cramps and a terrible workout. It’s taken me years to dial in to a full season-long understanding of what I need both on and off the bike. Experiment.