Can you convert all employees to nonexempt?

Q. For years, we’ve always had salaried employees. But we have many employees who always come in late and leave early. This is hard to track. We are thinking of making them hourly employees and getting a time clock. If I make them all hourly employees, I know that I have to pay overtime, but it might be worth it. Can I legally change their status from exempt to hourly, or are some employees required to be salaried? —B.B., New York