How long of a life is long enough?

Specifically, how long do I need to survive to get enough xp to unlock all the characters, and any other XP based unlocks?

I've got a camp set up such that I can basically go as long as I care to before I off myself to try one of the other characters. I'm only on my second "life" though, so I don't have any idea what the XP scale is.

Is 35 days enough to unlock everything, or do I need to keep merrily farming my way into the future, before stepping off the abyss and starting it all up again with someone new?

You gain 20XP per day survived, regardless of how many days have passed. This means that now, to unlock every character up to Wigfrid it takes 96 days. The detailed XP requirements for each character are the following:

• Wilson: starting character;
• Willow: 160XP;
• Wolfgang: 320XP;
• Wendy: 640XP;
• WX-78: 960XP;
• Wickerbottom: 1280XP;
• Woodie 1600 XP;
• Wigfrid 1920 XP (Reign of Giants exclusive).

At the moment of this update there are also three additional characters, but they're not unlocked with the experience points: two by playing the Adventure Mode, and the other one is unlocked by performing special actions in-game (only if you have the Reign of Giants expansion).