The solstice this year is at four minutes past midday on Sunday (21 December). I’ll be marking the end of the old year and the start of the new year, if there is such a thing. I usually tend to think of time as cyclical rather than as a succession of discrete units.
The only seasonal festivals I really recognise now are the two solstices marking the rise and fall of the sun, Beltane and Samhain as the beginning and ending of the fruitful season and a main harvest festival in August/September. Other than those, the only points I really take any notice of are the moon’s fullness and darkness.