I'm currently doing the SKE Biology course. I have a degree and PhD, but I have not been doing science at all for the last 11 years.
It sounds like you don't need the course, and my PGCE provider indicated that if completing the course was going to be a problem (due to current job), they could probably review the condition. I would definitely query it.
Having said that, the course has been really helpful to me in providing structured study (although I'm obviously far rustier than you). It sounds like the different subjects might be dealt with slightly differently; the first week looked at pedogogy but thereafter I haven't had to review lesson plans as someone upthread said they had to do for Chemistry.
Each week, the Biology course involves watching about 4 presentations (totalling about 1 hour), but periodically asking you to go and reasearch other websites for a more in-depth understanding. Then there is a session task, which you don't actually have to submit but you are encouraged to do so as they have little to assess you on otherwise. You also need to submit a self-assessment each week, but this is just going through their answers to the session task and scoring yourself red/amber/green for how well you felt you answered the questions, and identifying any areas for further learning. Most weeks, you are also asked to write a post on a discussion forum about a particular topic.
The key thing to complete is your Learner's Diary, summarising how you got on each week, any areas you struggled with, etc. You are graded red / amber / green for the Learner Diary. I think you'd have to submit nothing at all to get a red; if you only put in a paragraph you'll get amber; write 300-500 words that sound sensible and you should manage to get green.
Therefore passing the course is probably not difficult. For me, the course is taking a lot of time, but mostly because I'm taking extra time with extended reading, covering topics more in-depth, to make sure I feel confident beyond the course minimum requirements. I would guess that I am spending on average around 15-18 hours per week. If your course was similar I would expect that you could easily pass the course by spending 10 hours per week, maybe less if you just wanted to do the minimum to get by rather than spend time covering the topics in more detail.
Having said all that, Biology is obviously pretty different to Physics so it's very difficult to know how the courses compare.
Good luck!