If you can technically take to Jan off, I would do it. I would not give in to pressure just because they are short staffed, we always need more money of course, but if you are not quite ready/prepared, it is not in anyone's interest if there is a less than positive start.
It will give you time to plan your work/life balance. Everything can be organised now for next year, birthday cards, on line shopping delivery slot every week, cleaning plan, map out time for each child etc, time out when dh is there etc. Then discuss it all with gp and check it will work. Test run it even but with you having a day off not working. I do think some quiet time to plan this carefully will reduce your stress enormously.
Starting work before christmas will definitely add to your stress, because christmas is always so chronically busy. Buy the children smaller gifts but take them to lots of christmassy things like the christmas lights etc, and enjoy the time you have, don't think about Jan beyond planning for it.
Once Jan comes around and christmas has finished you might feel a whole lot more ready than you do now, and may even look forward to it. The key is organisation and feeling more positive.