Hi Darren,
The amount of time Fusion takes to generate a Movie depends on the what Movie Generation Settings has been selected.
For instance, Movie generated in render settings Colour Fill will be quicker to complete in comparison to Presentation Plus Render.
Higher Bit Rate would mean better video quality but will take longer to complete.
Higher Frames Per Second would mean, a smoother video quality but will again take longer to complete.

Larry Tamang
Fusion Support