By not working, I mean it's... not working.
Timescale misalignments are not subtle. If you have even a 0.1 timescale difference between the server and client, you get very noticeable jerking whenever you move, jump, jet, and with really large differences, turn.
EDIT: It also helps that getTimescale() is constantly returning whatever I last set the timescale to using /timescale.