That's what I assumed. The EU even alludes to intersteller communications being bad outside the Empire elite. So while the Emperor could talk to Vader one-on-one, any technology the rebels used would take days to months. The farther from the core, the worse as well. This is the reason Tatoonine, and so on celebrating at the end of Jedi makes no sense. The scene suggests that it's the same time. However, how can Tatooine know when Bakura, which is right next to Endor, didn't?