someone else may have another idea, but I think your temp may have been a half of a degree low though most of the hatch. Im just guessing, its really hard for me to tell on hatches I wasn't around. the symptoms match what you are saying though. some people also claim lack of protein will cause a hatch to be late - its a problem I haven't had so I am unsure. if ozexpat doesn't come back on here, PM him and have him review the thread. he is another very experienced hatcher.
i could be wrong, it has happened a couple of times in my life
. i know sumi and ozexpat are also very experienced hatchers. there are more who may have more experience, but ive never seen a post from either one that i questioned on the hatching subject.