Source: Externe

In Season 2, Windom Earle goes into the Lodge on March 25, 1989. Cooper follows them into the Lodge on the 25th too. 

In Season 3, the scene with Hawk going to Glastonbury Grove is very difficult to locate in the timeline. But his sentence "I suppose there's something to be happening here tonight" could indicate that he chooses that anniversary to come back to that place, after starting his investigation.

Source: Externe

Another clue is Mister C., saying to Darya that "tomorrow", he should be pulled back into the Black Lodge. According to my theorical chronology, that dialogue takes place the 24th, so it fits with the idea of an anniversary date on the 25th - maybe the date where "Saturn and Jupiter meet" once again.

However, nothing happens, because Mister C. had succeeded into escaping from the Lodge. Normally, he should have been pulled back, and "The Good Dale" released on that night, with Hawk waiting for him in Glastonbury Grove. As the Evolution of the arm said, "he must come back in before you can go out". The exchange should have taken place on September 25, 2016. 

Finally, the Good Dale got into the glass box in New York, then into the Purple Room, then took place of Dougie Jones, before awaking on October 2. Then he goes back into the Lodge, and comes out to meet Diane, possibly on the night of October 2.

Hawk going in Glastonbury Grove on the 25th fits with the structure of Parts 1-2, where the scenes takes place from September 21 to September 25, shown in a non-linear way.