December 1st's change isn't just for new customers. It's for newly-created or rescaled servers belonging to existing customers too, and it's plausible that those operations might happen a lot for some customers. And Thanksgiving and Black Friday are holidays for almost all American tech workers, so I'm not counting them as business days.
Normally that would be ok, but considering the way many systems are setup to load balance and quickly spin up new servers and spin down un-needed servers on the fly, one business day would not give you enough time to revamp your system to work with a different provider.