Utterly Mad

Hunger, Sleep, and Thirst: Each "piece" of the bar is an hour, so when an hour passes the Bar will go through its stages. You don't start starving, become severely dehydrated, etc... until 1AM the next day if you go without anything for a full day. Once you reach 'Zero' on the Hunger bar, you get a two day grace period in a weakened state to find something to eat, you move slower and people could easily overpower you. Same goes with Thirst, only instead you have one more day to find a source of water. And finally for sleep you black out when you reach 1AM of the next day or earlier depending on what you've been doing and your current fatigue; if you go without sleep for a day your fatigue meter is "cut in half" so you tire out a lot easier.

Bathroom and Hygiene: Bladder goes up every 15 mins and if you keep your hydration up (AKA: drinking tons of water) it'll increase every 10 mins for a limited time [meaning the maximum is 4 hours 15 mins which seems reasonable]; you'll have a 30 minute grace period once the bar reaches maximum before the inevitable strikes. Bowels go up every 25 mins [Maximum is 6 hours 25 mins], eating filling foods will drop that to 15 minutes depending on how big the meal; you get an hour grace period before the inevitable hits. And Hygiene decreases every hour you're out in the wilderness, so you'll effectively become a mess by the time half the day is over.