1) As long as the employee is paid in the next payroll (when the overtime should be paid), the employer may "review" the overtime to their heart's content, up to the last minute.2) Additional shift pay or shift differential is not required by law--employers may choose to pay it but do not have to. It being voluntary on the part of employers--and the law also not requiring all employees to be treated equally (that is, an employer may treat or pay similar employees differently, so long as they are not doing so based on a protected characteristic, such as race, sex, age over 40, disability or religion), an employer could give 1 employee the extra $1.00 per hour but not the other 2. (Unless there is a written employment contract requiring the shift pay; if there is, the employer must honor its terms.)