The second and third acts are not done yet, and there are still things to be done for act 1, so estimating playtime is difficult; 1/4 is the estimate of the content, though.
FWIW, the aim is to keep the playtime within 40 hours, assuming full knowledge of the plot and game systems, no crafting, etc, so that QA can do a full playthrough in a week. This was also the case for D:OS.