By my count Thursday 10-18 is day 21.We gave her the eggs at around 6:30pm on Sept. 26th.
You don't count the day you set, the next day is Day 1(I always miss that on mine).
They'll start to hatch between now and the weekend

21 days is an estimate.
Just listen for her talking to the chicks, then you'll know they've internally pipped,
then start listening for peeping. No Peeking! Good Luck!