Usually three to six weeks, but someone posted a thing from NBME from a couple of weeks ago that said that test takers in late May and June would probably not receive their scores until July 20-somethingth because they're doing some kind of scoring thing. Plus, this is the peak time of year for Step 1 taking, so I imagine the scoring people get backed up.
Most people in my class are taking Step 1 the last week of May, and they told us they expect our scores July 20. Last year one girl took it late (first week of July) due to personal issues, and she got her score at the same time as the rest of her class.