Tonight, December 25, is Nittel Nacht, a gentile holiday.
On this day there is an extra abundance of impurity and a stronghold of Kelipa. For this reason, the Jews throughout the generations took various customs upon themselves which are followed until this day, in order to diminish the spiritual power of the impurity.
It is the custom of many Jewish communities to refrain from learning Torah on this night so as not to add strength to the forces of impurity – kelipa.
This is the Chabad custom as well, and it is said that the Rebbe Rashab was not happy with those students who ignored this custom and continued with their studies as usual.
The custom to avoid learning begins from the night of the Eve of the 25th of December until midnight. Starting from midnight, one may resume learning Torah, and there are no longer any restrictions.
Many have the custom to play chess on the night of Nittel.

When does the eve of the 25th Start? midday?
Nitel nacht is dec 24 at night until 12am dec 25
shkiah
Isn’t the light and holiness of the Chanukah candles enough to be mevatail the tumah of this n8ght?
To note, the photo above of the Rebbe and Frierdiker Rebbe playing chess was not taken on Nittel.