Best day to beat 8th dungeon boss?

[☠Black Knight]

So I have done some reading, and from what I can figure out it seems like defeating Adachi will cause the game to skip ahead to Christmas. I want to get as many of my social links finished as possible. I have a few that are nearly finished, so those extra few days could mean the difference between maxing or not maxing the social links. But I was also told that I should try to beat him before December 22, for story purposes.

So, if I decide to wait until literally the last day and milk as much social link time as possible out of December... what will I be missing out on?

Also... since it's apparently somewhat relevant, Marie's social rank is maxed. And current date in game is December 21.

[GeassV]

22 for christmas event and 23 for last day finish dungeon

[1337Walrus]

Magatsu's deadline is December 24th. Finishing it on the 22nd is the only way to see the Christmas event and max your SL time.

You still have roughly three weeks in January to finish up any SLs, so I wouldn't worry too much.