About 10,000 visitors per day.
Six qualified recruits per hour is a minimum for effective live recruiting. (You’ll get some voicemails, a few folks unwilling to participate, etc.)
It's important to realize that this isn't just 6 responses per hour, but 6 potential participants who meet your testing criteria. We also look for a response rate of 1.5% to see if a screener is working. Putting those together, your screener needs about 400 views an hour for true live recruiting to work. Of course, you can still do a mix of live and scheduled users with fewer views per hour.