Medical experts usually say the average person can live for 4 to 6 weeks without food. The amount of time someone can go without water is much shorter, roughly a week (or less).
Your employer can force you to take leave at a particular time as long as they give you at least two weeks' notice. However, it is common for employer and employee to come to an agreement about the timing of annual leave. If you put in a request for leave, your employer has to have a good reason to refuse it.
Complete, sign and turn in your required paperwork within 15 days of informing your employer of your request to take a leave of absence covered under the FMLA. Keep in mind that it is your responsibility to turn in all of your paperwork in the time frame required by the FMLA.