Time? Well, it has to have progressed long snough for the initial anarchy to have died down and the leaders to step up. For example, i doubt Garn could simply proclaim himself Grand Moff without a few naysayers. And Ul-tera and the Ke'ter only took command after the Empire withdrew, so a new system of government needed to be set up. 
I think it's about twenty years after the Coup.