I'd think a year maybe 2 years on the DA era - 1st year makes sense of what happened when WizKids did to it. 2nd year shows the solutions to the problems created and sets you on course for the start of the second golden century.
(my take on what is likely to happen I did post on CBT forum)
One of the Clans takes Terra is declared ilClan. In the 100 years from DA-new era the old names Federated Suns, Draconis Combine, Wolf, Jade Falcon etc are forgotten as are the houses Davion, Steiner, Liao, Kurita and Marik.
Under The ilClan's stewardship a new golden age flourishes but individual nations disappear. Behind that however there is a growing resistance movement that is driven by individuals hailing from the "dead" Succession Families. As the timeline unfolds the ilClan falls back into the Terran Hegemony territory while the new Succession States rise up regaining their independence.
Pretty much the Clans do everything Nicholas Kerensky wanted them to do and then some, but in the end the Inner Sphere resets to what it was during the Star League-era just with a different nation in the middle.
(if this happens I will honestly shoot myself for working it out)