Employees who need FMLA leave must notify their employers either 30 days before, if the need is foreseeable, or as soon as “practicable” if the need is unforeseeable. Thus, elective surgery requires 30 days’ notice, while emergency surgery does not. Lots of employers, however, have far less formal rules in place. Some allow a simple doctor’s note to stand in as a request for FMLA leave.