Hatching Call ducks?

[GracefulBantams]

If I set Call Duck eggs on April 16th, when should they hatch? Since Calls are so super-hard to hatch, at what day should I intervene?

Thanks,
Grace

 

[SundownWaterfowl]

Hatch date would be May 12th, day 26. Move them to the hatcher day 23. Humidity should be around 75-80% during the hatch.