I would disrecommend quitting your job for multiple reasons:
1. You need the stable income to sustain yourself now and as much savings as possible for b-school over the next two years when you DEFINATELY will not be able to work. Work has to be your first priority at the moment, without it you won`t be able to survive.
2. GMAT can be surmounted with dedicated perserverance. Meticulously scrutinize your schedule, negotiate with your superior, use your sick days and vacation time, your lunch break, etc instead to find a way to squeeze out extra study time. I also have a hectic schedule like you (if not more so) but somehow, someway, I manage to eek out 10-15 hours of quality study time a week. You might want to even try text messaging yourself SC and CR problems so that you can study between guests, during coffee breaks, or whenever you have a spare 5-10 minutes. The key is to be the master of time management.
3. Quitting work means losing contacts and letters of recommendation from managers or coworkers who will inevitably have to support you in phase #2 of the application process. Maintain those ties and even start to think about who you will be approaching this fall.
4. If all else fails and you happen to already have a nice nest egg saved, then put in a request for a temporary semi-full time schedule change (35-40 hours a week) so that you can invest more energy into your prep. Honestly though, this should only be a contingency option if you feel yourself getting stressed out.
We are all in the same boat here, so remember to keep your head high and be the master of your time. You will prevail.