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.
You win some, you lose some. It works the opposite at the end of your trip, and you often can't gateway home the day you arrive. Old contract you had to finish before that 1600 local and could often get home that same day.