Yes, OP, you still have time to take a day or two off work, go cold turkey and sleep the whole time, waking up only long enough to eat a quart of ice cream. You will feel terrible for two days, as in, sad, otherwise not even sick to your stomach (except for all the ice cream). That's what you could expect after smoking a gram of crystal meth a day for months; I doubt cold turkey off Ritalin would be much worse. Compared to all the other things out there offering a rich tapestry of withdrawal symptoms to suffer through, this one should barely count. After a week off, you can resume your methylphenidate usage at normal doses, and probably be much more productive than you were at great overdose.
It's like all stimulants, even coffee: two cups may make you alert and running differential equations in your head like it's reciting the alphabet; but your four 20oz. Starbucks with added espresso shots just leaves you jittery with a pounding headache, growing anxiety with paranoia, and at the very least, needing to pee too bad to actually concentrate on test taking.
Like I mentioned, you may have just been saturating your transporters long before you ever got to 22 pills a day anyway, meaning you're technically not on as much as you think. And as long as you're on that much methylphenidate, you shouldn't expect to have much reaction to amphetamine, whether in Adderall, Dexedrine, biker speed or Vyvanse formulations.
One thing that definitely doesn't help with concentration is a benzo habit. Maybe, given your rising anxiety, they could do you some good; but a better option is still cutting back on the stimulants and getting some extra sleep. Benzos are no better than a shot of bourbon for helping you study. Quetiapine will actually counteract some of your methylphenidate mechanism (by blocking all that extra dopamine from activating certain receptors) at high doses, and at low doses is just an expensive, powerful anti-histamine. Those also aren't known for aiding concentration.
You have plenty of time to take a break and reset your brain. There's nothing to fear in just stopping the Ritalin tomorrow.