I have had Riley read his own science for Bigger Hearts for about the last half of it. He is almost 9 yo (the age Charlotte Mason suggested dc take over the reading for their school as they are able), so this has worked very well.

I think that it is just fine to have your dc read the science as long as they are reading it without difficulty. The science readings are pretty short, so this should not take much time.

After Riley finishes his reading, we go over the science plans in the box together, and then he works through it with me being available to help as needed.
It helps me to think in my mind which parts of a subject area are important for me to teach, and which parts are more their responsibility. In science in Bigger Hearts, my teaching part is reading through the box with Riley, and overseeing the follow-up science assignment. I have found that if I take a few minutes to read through the box with my ds, and we begin the assignment together, that he has the ability to finish the work independently, with me joining him at the end to help with any needed additions, editing, or changes. The actual time I am working with Riley on his Bigger Heart's science is about 8-10 minutes. What keeps this time to a minimum is helping him see the flow of the activity by reading through the box with him before he begins it, and then helping him get off to the right start. This is much easier than expecting him to do it all himself and then coming in later to have to redo things done incorrectly. If I was doing a textbook science, my time would be about 8-10 minutes as well, as the textbook really never works as a total replacement for teaching.

Science is a hands-on subject, and it really is important that this portion of the work is done. If you are having difficulty doing your teaching time for science, I would move it to first thing in the day. I try to do this myself with teaching times that aren't necessarily my favorite things, as I know I will naturally get them done if they are first.

I find my energy level going down as I come to the end of my homeschooling time each day, so it helps me to put more independent things last. Maybe switching the order of the day, and explaining their part/your part to the dc would help - I hope something here helps!
In Christ,
Julie