Like other types of jobs, teaching jobs should also have a stipulated number of hours. In universities and colleges, it is generally 6-8 hours of working which includes non-teaching responsibilities from Monday to Friday. Some universities focus on quality work and give flexibility to teachers but others do not and have rigorous rules to be followed strictly.
Well, to me and from experiences, working with international faculties, teaching at university level differs significantly from other levels, e.g. 12 levels and its below. I strongly disagree with the mind-set of leaving university campus after finishing scheduled classes. University teachers may not by any means be identified as whether or not they have any classes on any days of any weeks. You can be off-campus for a long, and so is for on-campus depending on necessity. It is not an 8 hours general duration based job. Unfortunately, the practice in most cases, has made it meant to be so.
Innovation is not something we can achieve with a time-setting mechanism. The typical practice of referred books based teaching is no longer sufficient. Researches, external projects, exchange programs both with universities and industries, development activities, and consultancy are a few key associate responsibilities that a university teacher may expose. However, it is also a relative thought since with that many support systems need to be in place and ensured. As long as anyone can not take this job seriously, the number of hours then counts. Generally speaking, the number of hours per week or day is not applicable in this profession.