The exact amount of time it takes to process varies, but is typically 3-4 weeks, and always is reported on a Wednesday, which happens to be September 1st this year. It does take a bit of time to process, so lets assume you want the score by the preceeding wednesday, Aug 25th. If you plan for a 4 week wait as opposed to the more likely 3 week wait, you should take it the week of July 26th, probably the 26th or 27th at the latest.
However, this might not be the best idea... why do I say this? Well, the biggest concern is if you don't perform well on step 2, you don't even have the option of NOT sending the score. That may or may not matter in your mind. The other concern/issue is that having the score exactly on September 1st will make NO difference. If you get the score on September 7th and just resubmit you score report after that (or set it to AUTOMATICALLY UPDATE - another possible mistake according to my first statement of why not), 99 out of 100 programs would not have even looked at your application by that point so would not have noticed the updated step score, and that 1 out of 100 that did happen to download your application will easily and without second though download the updated score and incorporate it without any consideration against your application. Really, as long as it is in there by late September for almost every specialty you gain/lose nothing, and really, if it is there by late October you don't gain or lose much of anything either.