Originally used to express a day that would never come, (for example "He can sit there until Tibb's Eve if it suits him, I'm not going!") Tibb's Eve, sometimes called "Tips" or "Tispy" Eve, came from the Newfoundlander's desire to start Christmas celebrations early.
In the past Newfoundland was largely Christian, and so Advent was observed across the island. Advent is a period of fasting and lasts for different amounts of time in different areas. For most it's not a full fast, but a time when you put aside luxuries such as alcohol, sweets, smokes, and other types of consumables. Many households would prepare various treats to look forward to at the end of Advent, marked by Christmas Day. These things would include fruit cakes, often soaked in rum, and home brewed alcoholic beverages.
Not wanting to wait until Christmas Day to start celebrating, Newfoundlanders moved celebrations to Christmas Eve, and finally to Tibb's Eve. Why wait to enjoy good food, good drink, and good people?
Though it's not widely standardised across Newfoundland Labrador, Tibb's Eve does some attention, though sadly marked by most as simply the second last day to shop.
Have a fantastic Tibb's Eve everyone!