You can take it in the summer, I'm guessing August, and still apply. When they only had tests in April/August, there were plenty of August-testers who were only affected slightly. However, there's a lot less room for error because you'll be complete around the end of September I'd assume. If you can't take it or don't do well, unfortunately, you will have to take two years off.
It's a gamble. You don't get a score back until September (assuming you take it in August). So your not fully complete at schools til then. And if you do poorly, there isn't much you can do except take it again in January for the next cycle anyway. It is a risky move.
an entire summer is plenty of time to learn the mcat material inside out. what you're contemplating is exactly what i did: mcat in august after graduating in june. however, i decided to wait two years b/c i wouldn't have been complete until october and thought that this would put me at a disadvantage. in the end i was insanely busy abroad and didn't get complete until august/september of the following year's cycle, without drastic consequence; i got into a couple outstanding schools.
point is: you'll have plenty of time to learn it all, especially if you devote yourself to it like a nearly-full-time job. as for the application timing, talk to your premed advisor - i think you should go for it. i could have done without my second year 'off'