ref, there's no pat answer to this. I think everyone is trying to give you insight.
When younger I worked at a company whose unwritten rule was "do what it takes", meaning long hours. The unspoken corollary to that was "if you don't have any thing to do, then take off". Fortunately, the work was amazingly fun and the co-workers were fantastic. Many late nights were spent. I didn't care that the salary was a bit less than I could have gotten at a less-fun job. I have fond memories of me & my co-worker looking at each other one afternoon, bored with nothing to do. We left at 230PM and spent the rest of the afternoon plowing through a couple of 12-packs. It was the kind of job where I couldn't wait to wake up in the morning because it meant I got to go to work.
I saw another organization, manufacturing, that was team-based and incentive-based. The assembly lines were all highly engineered, orchestrated, and timed. The people were actually running from station to station. It turned out that the incentive was 25%-30% of their base annual salary. All the laggards had been kicked off the respective teams by the team members. Those people were standing in line waiting for the gates to open every morning.
Then again I've seen places run by managers who looked at spreadsheets, but had no notion of the context of the numbers, nor of the way of producing those numbers or increasing/decreasing the numbers. Those were the places that laid down the edict of "## hours minimum expected per week". It was a hell-hole: unmotivated managers, poorly motivated troops, everybody spending their intelligence and talents trying to figure out ways to beat the system.
If you want the silver bullet answer, I'd say it is this: pay a fair (or better) salary for the time worked. Through culture, lay down the expectations of the number of hours that is acceptable to be successful in your business. Eliminate waste everywhere to reduce overhead costs. Do your job as a manager to create a positive workplace that allows talent to take root and flourish. And do your job as a manager and cull under-performing team members.
TygerDawg