Everyday -- whether it's peak or not -- preload start times (and how many employees are asked to work) are based on the projected volume for that day.
The Supervisor will receive this figure the day before and then based on that will determine a start time and how many people they need for that day.
They have a corporate procedure they have to follow. For example, if the projected volume for the next day is over 10,000, they must call in this many employees, if it's under 10,000, then they are only allowed to call in this number of employees.
That projected number is super important because based on it and it alone, the Supervisor decides how many delivery routes will be running that day, how many drivers they will need, etc. AND what the next day's start time will be.
You ain't gonna change their notification procedure, so don't waste your time trying. Accept it and be grateful they want you to come in.