If you apply for it tomorrow it can take anywhere from one week to 3 months after your scheduled interview.
Visitor Visa applications are subject to Name Check Clearance, now if the Consular officer determines depending on a applicants interview, situation, outcome of initial name check when you put your application in online by the Department of State, he/she can request one or many additional checks and until those are cleared, they will not issue a Visa.
Here's a hint, if at the day of your interview if they take finger Prints of only two fingers than your Initial name check with the State department is clear, but if they go for all fingers you already have a hit on the State department's initial name check and most definitely will be put in AP.
If the Consular Officer determines that a initial State Departments Name check is not sufficient, he/she will request more and put you in Adminitrative processing, that is totally his/her discretion and if he/she doesn't go for that than you will have your passport back in no time.
The last paragraph of information is only applicable if the CO decides that he is satisfied to grant a Visa to you at the interview, if otherwise then obviously you will be rejected.