You mean the complete game? Uh... Years, probably. Between 2 to 3 years is what I needed to complete my previous projects, but hard to tell at this point. If you mean R6, next month.
-Edit-
If by full you mean when the heroines will start become available, the first two relationships (Rias and Asia) will happen not too long after Riser's saga. Very close, and from there, as the story progresses, you'll "unlock" more heroines.