When is it too late to remove chicken eggs from broody?

[WhiteTreeOfGondor]

One of my Welsh Harlequin ducks has been broody today and could have started as early as last night. But she's sitting on a nest of combined chicken and duck eggs. I want to switch out the chicken eggs for a few more duck eggs but I won't have any more unwashed ones until tomorrow morning. Is 36 hours too late to remove the chicken eggs? I don't want to kill them if they've started developing.

 

[WhiteTreeOfGondor]

I actually just went ahead and took the chicken eggs out now. There were 4 chicken eggs and 2 duck eggs. Hopefully she'll let me stick a few more duck eggs under her tomorrow morning.