I know it is hard, but patience, patience, patience. If your average temperature during incubation is just a small bit low, the hatch can be late. My incubator was set a bit high and mine hatched a day and a half early. That was a surprise. Since they were all developing you are doing OK.
You say you are in day 20. Does this mean they have completed 20 full 24-hour days of incubation or have they completed 19 days of development and have started into day 20? If you set them on a Thursday, the full 24 hour days worth of 21 days of development is up at setting time Thursday. If you put them in the incubator Friday, then the time is up on a Friday. Many people get this confused.
Good luck!