Darly,
First & foremost -- RELAX! Stress & anxiety only make retention harder and recall less efficient.
Second, take it slow and easy. I stated prepping for COMLEX 1 on 1 Feb...I spent 2 hours/day M~Th (Fri was date night with the wife & 0 studying) and 4 hrs either Sat or Sun until 6 weeks prior to the exam. The last 6 weeks, I kicked it up to 3 hrs/day with 4+ hrs both Sat & Sun. And, I probably peaked too early! I ended up ess taking the last week off prior to the exam...burned out!
Third, don't bog down in all those subject specific board review books. They are written in far too much depth for actual review for the test. Focus on First Aid: Step 1 & Step Up to the Boards. If you've read them...read them again & again. Use the subject-specific board prep books as references to look up things that are a little fuzzy (I used the BRS series)
Fourth, quiz yourself frequently. I used Buzzwords for the Boards...my study partner and i would get together about 2x/wk and simply open Buzzwords, 1st Aid or Step Up to a random page and quiz each other. Also, if you prefer to work solo, there are a number of CD-Rom test simulators. I liked Kaplan's and the NMS versions.
When to take the USMLE? Take it SOON after/before the COMLEX. I screwed up, put it off and will only just get to taking the USMLE on 17 Jan. Believe me, once you hit the wards, YOU WILL NOT WANT TO BE PIDDLING AROUND WITH THAT BASIC SCIENCE CRAP, you will want to be reading about diseases and treatments...not freakin BioChem pathways!!!!!!