No, it is not legal: overtime must be paid for all time in excess of 40 hours which an employee works in one work week. If one payroll was missed due to a technical error or the employee not documenting it promptly, it can be paid later--but must be paid. If the employer will not pay, you could contact your state department of labor to file a complaint or sue for the money--whether it is worth filing a compliant vs. your employer or suing them over an hour-and-half, however, is a different story.