I am glad I am not the only one interested in this. I logged on yesterday and played for a few hours and started a class I haven't played yet. I got CNJ to lvl 15 and I still have a red xp bar. I logged off without resting, I am going to try to use up the bonus I have now so I can work with smaller numbers. So the numbers I have now have not been calculated because I havent emptied my bonus yet, but they may be interesting.

roughly 130hrs of rest time
62250 xp gained
still in the red

Also, for anybody who may be wanting to kinda figure this out, I should point out what Peptaru mentioned. The amount of xp the rested bonus covers on your xp bar is 3 times the amount of bonus xp accumulated. to use his example, if the glowy part covers 1000 xp, then the bonus gained is only 333 (roughly) xp.

So when I finally deplete my current bonus, I will divide that number by 3. And since I have about 130 hours of rest time, it may be that the cap is somewhere in that range, so referencing smaller calculations to this one should tell us either where the cap is (if it is inside 130 hrs), or that the cap exceeds 130 hrs.