That depends what stage of the interview you're at - you can perfectly reasonably start the process with as many as 15 or 20 and just plan to winnow them down.

That depends what stage of the interview you're at - you can perfectly reasonably start the process with as many as 15 or 20 and just plan to winnow them down. You definitely wouldn't want that many on site interviews, but if you just do a recruiter phone screen and hiring manager call for each, that's still <40 hours per week. If it turns out everybody loves you and wants to advance you to the next round, just pick the top 4-6 (or however many you feel like you can handle) that have the best combination of hiring manager + company/product and move forward with those.