There is no federal law stating how many hours exempt employees must work per week. In most cases, they are expected to put in as many hours as necessary to complete their assigned tasks and carry out tasks.
They get paid for getting work done regardless of whether they worked for less than 40 hours a week or more than 50 hours per week.
However, some employers require exempt workers to work 40 hours per week. In companies with such a policy, employees may monitor attendance and take disciplinary action such as job termination on defaulting employees.
However, they cannot deduct pay simply because the employee doesn't work 40 hours per week, which can disqualify the employee for exemption.
Some companies also compensate those who meet or exceed 40 hours per workweek. This depends on how the company policies on rewarding employees.