I have no experience hatching, but found this post and wanted to send you a Welcome!
glad you have joined us.
So sorry about your past losses and wish you success with the current attempt.
Hopefully someone with hatching experience will show up with an answer.
Please consider posting an intro under the New Members forum to get a proper welcoming.
Congratulations! Here's a link to help you decide when to take out the hatched babies ...http://www.backyardchickens.com/a/how-to-incubate-hatch-eggs-just-21-days-from-egg-to-chicken