Amen to this, brother. Maybe the general problem here is that the people who are doing the interviewing aren't the same people who are going to be working with the guy getting interviewed.

In short, no. I tend to run out of steam after about four or five hours, having to stay an extra three or four hours after the eight would just be a waste of time, piss me off and not get anything accomplished. Additionally, he's basically asking you to increase your work time by at least 25% for free. Nice try there, buddy. Assuming your boss is a reasonable human being (a little difficult to believe considering he even suggested this), you should be able to convince him that this is a horrible idea. Otherwise, start polishing your resume, it's time to jump ship.