Mine have started sitting with around 20-30 in the past. But if you have more than one female, the others will keep on laying in the nest while she's setting. So you may want to mark the eggs yours starts with, and pull out any new ones that appear. You'll have to be sneaky and do it while she's on a food break, preferably out of sight.
We did not do this for our hen that was just setting, and ended up with only 4 keets out of a nest of 40+ eggs. It was a "live & learn" thing for us, next time we'll know better.