While sacrifices might be made on special occasions, such as the arrival at a holy place, the setting up of a new house, victory in battle, the opening of the Assembly, or the death of a king; and might also be carried out by private individuals; there were regular feasts in which all the community took part. It also depended on how far North or South you lived as to which seasonal holidays you celebrated. The fixing of these must have come about long before any formal calendar was in use, although by the first century AD the Celts in Gaul seem to have possessed an elaborate one.
Before such calendars existed, the feast were presumably at the points of the seasonal round important for farmers, herdsmen, hunters, fishers and warriors, and could be roughly reckoned by observation of the moon or the planets.
The Celts and the Germans used the half-year as the basic unit of time. In Iceland the misseri (from miss, alternation) were summer and winter, each season 29 weeks in length, and the beginning of each was marked by feasting and religious ritual. The passage of time was noted by counting winters and nights. Julius Caesar noted that the Gauls held that night came before day, and kept to this when celebrating birthdays and the beginning of a month or a year, just as for xtian Christmas begins on Christmas Eve. Tacitus noted similar with the Germans: ‘They do not reckon time by days, as we do, but by nights'.
This implies a period set apart for feasting by the whole community rather than a particular entertainment when guest where invited to the kings hall....
....but the sacrificial feast can be distinguished from banquets in general because at this men partook of animals sacrifice to the gods, and drank mead and ale in the gods honor. They met to renew their contract with the supernatural world, and to ensure good luck for the coming season, and this was something for the whole community to share in and not for selected guests. Games and contests might form a part of the feast which would last for several days. The essential element, however, was eating and drinking together, and there are occasions when strangers were not admitted: One such reference is in the Austrfaravisír, written by the Christian skald Sigvatr after a journey to Sweden in the autumn of 1018. He recorded how he was refused entry to several farms as the álfablót was being held there. The natives of the land drove the poet from their homes. At one farm, the housewife was standing at the door and refused him admission stating that she feared the wrath of Odinn. Her household was heathen and she was holding a sacrifice to the alfs, an álfablót.