Hub and Spoke is designed primarily for data restriction requirements (where data cannot leave a country/area/etc, and the Hub acts as a central point for all Spoke servers to communicate back to for a single overview.
Foundation Data is contained and distributed to the Spoke Servers, however there is still local Foundation Data that can be configured on a Spoke server that will not participate in the Hub operations - this is dependent on the Company type chosen when configuring and from where i.e. Hub or Spoke.
It should not take too long to configure if the system is already installed, however the DSO for the data from the Hub may take some time dependent on the volume.
Synchronisation occurs once the Spoke is setup, you manually invoke this so you can target particular Spokes however I am not sure on if they automatically participate in the Spoke > Hub operations by default (I think they do once registered and data sync is done to move the Foundation Data over from the Hub).
All relevant information is available on the document Wiki: