How long to wait on a brooding hen?

[Pupsnpullets]

My hen has been setting for what seems too long. I had a dozen eggs under her and one broke a few days ago. It had an embryo in it. According my calendar she should have hatched a couple of days ago. In fact, Wednesday was the 21st day. It's now Saturday and nothing. It's possible the chicks have died in the shell How much longer should I wait before giving up? Poor little mama hen.

 

[BoomChickaPop]

What breed is she?
And have you candled them?

BCP

 

[Pupsnpullets]

No, haven't candled them but I know from past experience they have at least partly developed. She is a full sized mixed breed with the same under her. Thanks for responding

 

[BoomChickaPop]

You need to candle them to see if you see movement.

BCP

 

[Pupsnpullets]

Will do, and thanks. Is it normal for them to go this long?