Is this happening anywhere else?
During the winter when driving condition are getting bad they will send out a messages similar to that.
That doesn't mean you have to deliver all your packages by that time it just means you need to be off the clock by that time. So you Deliver what you can and sheet the rest as missed or how they tell you to... Don't jeopardize your safety to make there numbers work.
It all comes down to they just are trying to limit what they are paying in OT...