I won’t bother reading the entire thread until now, so sorry if my answer is repetitive…
In the time of the Alter Rebbe there was a group of Jews called “misnagdim” (mitnagdim in sphardic Hebrew), who called themselves thus on account of their opposition to the ways of Chassidus, since at the time it was still new and they had some shaalos on it. These mitnagdim were the ones who, for example, made a libel against the Alter Rebbe in order to send him to prison in the first place.
When the Alter Rebbe was released, he was supposed to be sent to the house of his chossid (the name of the chossid escapes me at the moment), who lived on the top floor. The authorities who escorted him, however, accidentally brought him to the same address, but the bottom floor, where there lived one of the more serious misnagdim. Well hachnasos orchim is hachnasos orchim, so he served them both tea, but commenced to berate the Alter Rebbe’s rabbi and teacher, the Maggid, and the whole tnua of Chassidus in general. The Alter Rebbe listened and did not respond with his head buried in his hands.
The chassidim who were waiting upstairs eventually realized what must have happened, and went downstairs to rescue the Rebbe…The Alter Rebbe said something about showing kavod to baal haachsanyia (if any of these details are important to you I can look up the sources…), made a brocho and drank the tea, then left.
Since it was already after shkiya by that point, and the Alter Rebbe technically wasn’t “freed” from his imprisonment until leaving the house of the misnaged, where he had to suffer hearing so much against his teacher etc., then it is considered as if the “finalization” of the geula was on chof kislev.
Today B”H no misnagdim exist, since all the shaalos and kushyos they had were answered on several occasions (the debate in Minsk, in Shklov, and others, with the Alter Rebbe himself), and Chassidim and Litvaks have had numerous opportunities over the years to work in full cooperation with each other. Any hisnagdus on anyone’s part today is simply a matter of ignorance and nothing more.