"[An] eligible employee with a serious health condition that necessitates limited hours may use FMLA leave to work a reduced number of hours per day (or week) for an indefinite period of time as long as the employee does not exhaust their FMLA leave entitlement.... The employee may continue to use FMLA leave until the employee has exhausted their entitlement to FMLA leave.... [If] the employee never exhausts their FMLA leave, they may work the reduced schedule indefinitely.... [T]he requirements and protections of the FMLA are separate and distinct from those of the ADA, and an employee may be entitled to invoke the protections of both laws simultaneously."