What exactly is departure time used for?

So I set up low cost charging and it makes me set a departure time.. I just set it for 9AM every day... I know its suppose to do some kind of warming up of the battery...

My low cost charging time is 12AM to 6AM... Is there anything bad for setting a 9AM departure time? Sometimes we drive at 10AM, sometimes we drive at 8AM.. sometimes we dont drive for the day. Do I need to change my departure times?

You can activate / deactivate preconditioning, which will follow these times. Otherwise, the purpose of the departure time (misguided, I believe) is so iDrive can calculate whether the battery can be charged to 100% during the low-cost time slot, prior to the set departure time.

If the battery can be charged with the available amperage, great, the tariff time slot function works as expected. If it calculates it can't reach 100% during that window, charging begins immediately.

The system design makes a lot of priority assumptions which I personally don't agree with, but that's what we're left to contend with.