As per An Post’s schedule for Christmas post, the last date for posting online orders for delivery to Ireland and the UK is 18 December. The last date for posting to Europe is 15 December and for further afield (including the US) is 6 December.
Based on previous experience books posted later than this simply get stuck in the huge volume of material moving through the postal system in Ireland and abroad around the Christmas period.
Any orders received after 18 December will be posted in the New Year.