This is about how long it’ll take to finish researching Tribal Era innovations.

Ideally, if you start the game in 867, you should aim to switch from Tribalism to Feudalism around 1050-1100. Raid, raid, and raid some more because when you switch to Feudalism, it’s all over. You should use the advantages of having a Tribal government to fill your coffers and gain Piety. There’s a fairly natural progression to change from Tribal to Feudal in Crusader Kings 3.