How far in advance do you need to make a cake

For holidays, they need a week. For cakes at least two days.

I've had one made in the same day as ordered.

We always give atleast one to two weeks. For birthday cakes that has a kit we like to give a month just to make sure the kit is in if not give plenty of time for it to be ordered.

Birthday cakes can usually be made the same day...special cakes, about 2 days notice.

Asking in advance is good for holidays

Usually it's next day. At least in the Times I've had cakes made.