When I am very dehydrated, it takes days to feel normal again. On hot rides with substantial climbing I usually come home 5 or 6 pounds light, but I have finished 11 pounds light. That's around a gallon and a half! Since the body can only absorb around a quart per hour, at best, it's going to take an effort to put back 1.5 gallons.

I think the color of your pee is a good way to check to a certain extent, but if you're really dry and you pound down a bunch of water, your pee will be clear and you will still be dehydrated.

I agree about the electrolytes and minerals and I feel best if I keep eating during the ride, (regular food), and I love a big bowl of soy ramen at a Japanese restaurant after. It's salty and has liquid and carbs, yum.