How long to do one lesson in Considerng God's Creation?

I just received a used copy of Considering God’s Creation, but it is missing an introductory page, which would probably answer my question. I was wondering how long it typically takes to do a lesson. We are not using 106 Days of Creation. We are only using CGC.  Do you do one lesson a week? Do you do CGC every day, or maybe just 3 days a week? I want to start tomorrow, so I need to have an idea of how much to do in a day. My daughter is 12, so she may be able to handle a little more in one day, but I don’t want to rush through it.