Well after setting 40 eggs in the incubator I think I have one going broody. She seems serious and so I just keep putting eggs under her. Lol she is small but I think about 25 will do the trick. Lol
25 eggs would be too many for all but the largest hens.... and doubtful then, unless they are small eggs. A hen should fully cover all eggs of her clutch at once, any which stick out around the edges are prone to chilling and may develop slower or not at all. A hen will try rotating them around so they get some warm time but often it ends up reducing the hatch rate overall because even more get chilled. For best results it is suggested that you place a reasonable number to start (say 12-15 for a large hen) and then once she settles on them you can add more a couple at a time until you notice they are no longer completely covered, stop there and remove one or two so she isn't overcrowded.
You can keep the rest in an incubator and if you candle the broody hen's eggs about day 10 or so you can pull the ones which didn't develop (if any) and replace them with ones from the incubator.