Excess insurance help

Can someone explain how it all works? Do I need to get it before the cars delivered on Wednesday or can I have it starting from the next agreement signing date ie next month ?

You need to have it before the car is delivered to get immediate coverage. If you wait you will only be covered from your next renewal date, or vehicle swap. Any damage or insurance claim that takes place in the first month wouldn’t be covered if you don’t sign up ahead of delivery.

It would be strongly advisable to do this sooner rather than later for peace of mind, rather than being £1000 out of pocket if something happened shortly after the car arrived.