I'd suggest telling your boss that it's really important that you get [choose date here] off because you have a job interview.

Or asking your boss if he/she would be willing to be a reference for you on your resume.

If you boss asks why you're are considering leaving the company tell him/her that you are looking for a job that only requires 40 hours a week because the constant onslaught of 60 hours a week is leaving you feeling burnt out. That should get the message across!