I'm still of opinion thatvshpuld of told the mum, but whatever.
While a chapter a week is nice, I think it would put pressure on you to fill it out, and only a 1/4 id also bit silly.
You could also do half chapters evey 2 weeks.
But I'm happy to wait a month for a full chapter.
Personally, I would prefer what is easiest and most comfortable for you to do.