Honestly I've never times it and I don't think anyone has because everyone's play style is different.
The inquisitors own class story is already over.. once you finish Corellia, defeat thanaton the class story is over.
From Ilum onward your in the shared story that all classes go through and it's the same story for all.
With the exception of separations between republic and alliance stories where the split is based in the faction and not the class like the Rise of the Hutt cartel has two stories. One for Republic and one for Empire. So all republic classes share the same story and all empire classes share the same story.
There isn't really class stories any more after Corellia. There are some class quests here and there, class specific dialogue but that's it.
For the whole story over all, definitely over 100 hours worth but there is no known exact number.
