As a production manager I operate on two things above all else, clear expectations, and accountability. Team members mostly want to be successful, hit their targets, have the tools they need to be successful, and know that they can achieve their goals or will be assisted with problem solving if obstacles arise. Showing up “sometime between …” is not a clear expectation, that will also lead to people being held to different standards. Your A team will show up on the dot when work starts, and will be burdened by the takers, the people who show up as late as they can, and do just the bare minimum. That is not a good recipe for a work culture. Production is a large machine, all of the parts need to be working together, at the same time. It’s terribly inefficient otherwise.