It depends on how long she decided to wait to climb into the nest box. Some of mine jump in 10-15 minutes before its ready to pop out, others will sit for an hour or so. I'm not an expert on this. I'm just going by what I see my girls doing. Sometimes mine just like to psych me out. They go in the nest box for a bit, then jump out squaking like a banchee - and there's no egg.