We know that on the 10th day of the Mahabharata war Bhishma went down in arrows. War continued for another 8 days (Day 18).

After this Yudhistira went to Hastinapura, returned; Sthree Vilapa; Shanti Parva and Anushasana Parvas. At the end Mahabharata says, after 50 days Yudhistira returned to Bhishma preparing for his death. Bhishma dies on Magha astami.

Question is how much was time between war ending and completion of the main discourses in Anushasana parva (the red box in below picture)?