Since I don't think there has been a formal discussion on the DxD timeline. Why don't we start now?
Here are the definite dates mentioned that's on the top of my head.
- Asia and Issei met late April
- After the Gremory group presented themselves together with the other rookies in front of the higher-ups and returned to the Gremory palace, the date is July, 28. And the Rating Game will be held on August 20
- At the very start of Volume 17, almost 4 months have passed after their house was renovated.
- The events in Volume 18 happened right around Christmas.
Start from there and create conjectures that will be agreed upon by the whole community.