Depends on how long you are giving to studying for the USMLE. Basically, I would start using QBank from day 1 of your study plan.
I'm gonna say start using it exactly one month before you take step 1, unless you splurge for the 3 month subscription. I wouldn't recommend the latter, I know a bunch of people who paid more for the 3 or even 6 month subscriptions thinking they'd use it long ahead of time only to realize that doing Q-bank while finishing your 2nd year classes sucks. Practically nobody used it to any significant degree ahead of time.
I used Qbank to study for exams during the school year, so you could try this if you think it will help.
I started it in the end of Feb. It has really helped me out alot and I have been watching my scores steadily rise. My school bought everyone in our class the USMLE Qbank as well as COMLEX qbank, so i didnt have to worry about cost. It has helped me prepare for the 200 question comprehensive exam i took today covering 2 years worth of preclinical classes.
