Site: nolo.com
... For example, if your company requires one week's notice before employees can take vacation time, and ... Once the notice week has passed, you are entitled to use your vacation time. ... Scheduling and Notice Requirements
The FMLA requires you to give 30 days' notice of the need for leave ... If your need for leave is not foreseeable, you are required to give as much notice as is both possible ... If you have a medical emergency, for example, it might not be possible for you to give any advance notice ...