Have they set yet? (your post was 3 weeks ago and I only just saw this) Weather is certainly a factor, but so is personality.
I normally collect my Muscovy eggs and leave them a couple of golf balls. When they start leaving down in their nest, that's a signal they're thinking of setting. Day 1 a little down, day 2 lots of down, day 3 you'd better be ready to very gently put your hand under her to swipe the golf balls and replace them with 8-10 of the eggs you were saving. First time moms usually get fewer, more experienced moms get more.
I *always* put my hens in protective custody. If you go to this post:
https://permies.com/t/141128/Trouble#1107818
you'll see what my set-up normally looks like. You want to keep the other hens as well as the drake from hassling her or adding extra eggs to her nest.
Hopefully the girls were just waiting for warmer weather and have decided the time is right already. I trust you do know that they take 5 weeks to hatch? I strongly recommend you start a spread sheet of date of setting, # of eggs (but be aware they may drop another egg or two after setting) and expected due date. Two days before they're due, I put a small baby waterer and feeder in. We just use
unmedicated chick starter crumble - chicken meds can kill ducklings - as we know they'll be out on grass the day after hatching so any extra vitamins and minerals will come from the environment.
I use my Muscovy to hatch other eggs also. Two days ago Bishop hatched out 4 Khaki Campbell/Golden 300 crosses and they're already in a bottomless portable
shelter learning about duckie bathtime and how to poke in the dirt. Muscovy ducklings are pretty sturdy little things.