In the context of people wanting to go for clinical psychology, I have been asked this question a few times over the years. But also have seen how it plays out. In my experience the answer is dependent on the capability (and expectations) of the asker.
The people who have made job + OU work succesfully are usually strong students who are academically minded and already have very good study skills/ time management. They also usually have no other obligations (relationship to maintain, children to look after, carer responsibility, financial pressure to focus on earning). They are able to focus, set boundaries around work and study, and then stick to them. They are aware of the competition and realise the OU degree is basically a ticket to enter the race, but it's what happens around that degree and afterwards that counts more. I think for this group mentoring from someone already in that field can be really helpful, as it maximises time and effort.
The people where I have seen it go badly tended to be those that aren't academically minded or have poorer time management and skills. In addition, many haven't fully thought it through, have lots of competing demands, are not being realistic or are trying to do it on an arbitrary timeline.
"What is the minimum time I can take/ have to do?" is usually a red flag, because their competition don't that mindset. They are up against the mindset of "I will do whatever it takes- plus more." When it comes to sorting through a pile of 100 DClinPsy application forms this mindset really gets highlighted.
That stuff aside, I think the most reflective thing to do is to consider the other things you need to do in the upcoming years you mention, and what level would you would be willing to sacrifice those for your plans in psychology. I am by no means saying you should prioritse psychology btw it's more about what you want and what will be best for you. The decision will be very different if your list goes 1)Psychology career, 2) Marriage, 3) Children, 4) Travel, 5) Buying a house, than if it is the reverse.