Not an MS1, but im one of those people that suggests preparing for Step 1 from the start of school. Float by and pass your internals, but the more time you dedicate towards Step from the start, the better position you'll be when the time comes for the only exam that matters.
Use zanki from the very beginning, and use Boards and Beyond as you're going along, and you'll be in a superb position by the end of the year.
Use zanki from the very beginning, and use Boards and Beyond as you're going along, and you'll be in a superb position by the end of the year.