When an employer dictates that a worker must work certain hours, it is evidence that they are an employee. But, the opposite is not true -- employers are not obligated to dictate the hours of their employees.
The fact that most employers do dictate hours is a function of those job expectations, not their legal employment classification.
It is pretty common for mid or senior level white-collar salaried jobs to have a decent amount of freedom in working hours within what is functionally reasonable for their role.