Only you can set your stint lengths. It honestly comes down to how long you can stay focused and not exhausted in the car. I have done as long as 4 hours in the car before and man does that put a beating on you. I came into the pits thinking "yea, I could go another 30 minutes", and then almost collapsed once the adrenaline wore off. Our strategy this weekend was to put someone in the car for 3.5 hours, then swap in my sister to drive as long as she could, then have my brother close out the day. Repeat the next day with the 4th driver opening for half the day and then repeat the afternoon. That 3.5 hour stint is very long and very abusive on the driver.
2 hours seems to be a decent length for balancing abuse on the driver and minimizing time stopped.
Put water in your car, just do it. Doesn't matter how. We have a bucket hung behind the driver seat where we dump a camelbak bladder. Swap it out at driver changes. Putting a good cup holder special built for a large bottle as mentioned also works. Some people have gone as far as a low pressure pump and tank for water on demand. Doesn't matter how, put water in your car. Even in the fall when it's cold you use a lot of water doing this.
If you run in any kind of heat, get a cool shirt system. I won't even get into the car during the summer without one. We had one race where the pump acted up and failed on one of our drivers. He realized at one point he couldn't remember where the track went, somehow found pit off, parked it in some random team's space, and stumbled back to our paddock space. He got heat exhaustion or worse, and it was scary as hell. I've never let someone go out in the summer without a functional cool shirt after that, and now we have a pit space system you can clip into after driving to help cool off again.
20+ Time Loser
FutilityMotorsport Abandoned E36 Build2008 Saab 9-5Aero WagonRetired -
1989 Dodge Daytona Shelby 2011-2015 "Lifetime Award for Lack of Achievement" IOE, 3X I got screwed, Organizer's Choice