You definitely have time to do these things, assuming that you're not intending to apply to a ton of schools, however you definitely should get going. You might need between 1 and 2 months to prepare for the GMAT depending on what score you're gunning for.
Whether you quit work right now to focus on apps, probably depends on how much cash flow you require, how many hours work demands, and how much you have to prepare for the GMAT and other items.
Ideally, you could work on multiple items at once (e.g., study for GMAT while selecting recommenders, while reviewing essays). Most are able to balance work with application prep. For me, I was able to do consulting while preparing my app, but I spent every free moment working on my app.