Security clearances take anywhere from 6-12 months to clear completely. You won't be fully-cleared until you've started at USUHS. What USUHS will do (at least to the best of my knowledge, don't quote me on this) is they'll run a rapid investigation and grant you an interim clearance. As long as you aren't actively using drugs and you aren't a felon, you'll be fine. Don't lie on your SF-86. If you're currently using drugs (this includes using someone elses prescription medication i.e. Adderall), stop using now. Make sure you save a copy of your SF-86, as you'll need to complete it again down the road. Make sure all of your dates add up. What I'd recommend doing is creating an excel document with two sheets - one for all of the jobs you've had for the past 10 years, and one for all of the places you've lived in the past 10 years. Have a point of contact for each listing. This will help out big-time when it comes time to fill out a SF-86.