Do you mean safe - as in will they all have lambed? Perhaps if you sure that all ewes were tupped before 7th December. But even then they can be late, and even if they have all lambed there can be a lot of care required until lambs are well grown. You may have to bottle feed, and you will have to look out for mastitis and all sorts of ailments. Personally I couldn't go away at that time unless I had someone that was experienced and that I trusted explicitly!