QUESTION

Can we classify our assistant managers as exempt from overtime? We pay them a salary.

SHORT ANSWER
The title of an employee does not determine whether they are entitled to overtime. It depends upon factors such as the amount of direction and control they have.
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Exempt status of employees depends not merely on title or the fact that they are paid a minimum of $455 per week on a salary basis, but on how much direction and control they have in their position.  Is their primary duty management? Do they regularly direct the work of other employees? Do they have the power to hire and fire other employees?  If not, exempt status is unlikely.