With Christmas only a week away, it is important to ensure that you make any last minute orders or posting out of Christmas cards in plenty of time. Some companies will offer a guaranteed delivery for Christmas by a certain date which may well be in the next day or so. If posting Christmas cards using the royal mail then you should allow at least 4-5 days for 1st class post as although it is normally within a day or two, the Christmas post tends to get a bit delayed.
If you have left it late but need to guarantee delivery for a certain date then you may wish to choose one of the royal mail guaranteed services or a third party courier. You will pay more for these types of services so if possibly post early to cut down on costs.
If you have a number of cards or presents to be delivered in close proximity to each other and your location it may actually be more cost effective for you to deliver them yourself.
When using a courier, see what tracking services they offer and what happens if a delivery deadline is missed. Many will even offer live tracking where you can see where the parcel currently is and how far away from the destination it is.