I always have this confusion, since I assume the app scripts are code running on google servers located in california.
However, I had run as methods (doGet/ doPost) after a web deployment. It gives me my locale date. (https://script.google.com/macros/s/AKfycbxhzHRji1XLgmOJL1hJ9MZJVDsWSHm2errtakBn8OORmn2MTt0/exec). Not sure if this is exactly my os date.
Is this value likely to change for any reason such as the request being load balanced? How is it getting the date of my locale?