Originally Posted by zerozero

The 0700Z start time is to protect those on the west coast from starting excessively early on an X day.

Examples for ANC/PDX/ONT/LAX bases:

Old contract: Your first assignment has you duty on at 0100Z on your first work day. In the winter, ANC is UTC -9. That means you would duty on at 1600 local on your OFF DAY. Not cool.

New contract: You duty on at 0700Z (2200 local) and the local day is marked "WORK", not cutting into your X days at all. Much better.