A single Blockland instance can only have a single timescale.
Each client is an individual instance, thus each client can have it's own timescale.
However the server is also an individual instance, but only a single one, thus it can only have one main timescale.
We currently have no way of modifying the engine (well, we do, but not in an add-on), and engine changes are required to let a single instance scale time differently in different areas of the world.