That sounds about right. They will only sit on the nest for that long if they are broody. Do you have a broody? If you have any doubts about whether you have one or not, then you don't have one. Broody hens are pretty distinctive in their behavior. I had never seen a broody hen before last year. My girls are not prone to going broody, but last year one went broody on me. It took about 2 seconds of watching her behavior to say "Oh... so that's what everyone was talking about when they said 'broody'."