Do broody hens need the full 21 days

[Amyloo]

My 8 month old Araucana has gone broody for the first time for the last 2 days and I have a clutch of duckling due to hatch in the next day or so. Is it too soon to put the eggs under her or will she reject them as she hasn’t had the full 21 days and she is so young?

 

[DobieLover]

My 8 month old Araucana has gone broody for the first time for the last 2 days and I have a clutch of duckling due to hatch in the next day or so. Is it too soon to put the eggs under her or will she reject them as she hasn’t had the full 21 days and she is so young?

If she is still a dug in broody in a few days you can give her a try. Duck eggs are larger than chicken eggs so she won't be able to hatch that many. And she should be set up in a ground nest if she isn't already.
She may break if you move her to a ground nest.
If you want her to try, I'd get her moved to a ground nest now. Put it in a secured area so she can't get out until you let her out and others can't bother her. Either she'll graft to the new location or she'll break.