I have been using the Old Farmer's Almanac to find my dates for gelding and weaning. I use the same for both. I wait till the sign is below the secrets (Scorpio) and in the thighs (Sagittarius), knees (Capricorn), legs (Aquarius) and the feet (Pisces). I try to not wait till the last day when I can.
Doing it my way, here are the dates I would geld. Dec 1 thru Dec 5 or 6 --- Dec 24 thru Jan 1 or 2 --- Jan 20 thru Jan 28 or 29.
I have had great luck doing it this way and was better able to schedule the vet because I gave him more days. (I usually didn't give him the last two days as options so if he pushed me a day past my request, I still got in the timeframe) We have had probably an average of 3 or more most years and have had no major problems to date. I also have had great luck with weaning these days. Not much fussing, mares dry up nicely and foals eat and drink well.
Good luck
Angie