... make any party you have, when it is NOT nap time. Otherwise, your child will be too tired/fussy for a party and be among lots of people & noise and get over-stimulated/fussy. The 'timing' of the party is very important. AND.. you also have to factor in clean-up time too.. .and putting away everything and I would... designate that you WILL need help with that... since you also have a 1 year old to care for. Otherwise, cleaning up after the party, will take as long as setting up everything... and that can take up a LOT of time. Plus with the actual party time.
DESIGNATE on the invitation... the "start" AND "end" time of the party. Otherwise, you will have a LONG drawn out party... and a tired 1 year old. Usually, parties at this age or even older kids, are 1 hours or 3 hours max.
Also, Halloween typically means, that families may have other plans with their own kids, their traditions, and going out in the neighborhoods, or going with their own friends and going to other classmate parties. As such, I would not plan the party for night time. So that it does not conflict with other kids/parents usual plans for Halloween....
Just a tip.
My Daughter, is born around that time.
all the best,
Susan