As a rule of thumb, each 'point' allocated to the course is roughly ten hours studying. So a 60 point course is about 600 hours, spread over about 9 months, which works out at about 16 hours a week.
In my experience (I've been an OU student too) this is quite a good estimate. Some sections of the course might take less time, especially if you're more familiar with the material. But there are always sections that are harder which take longer .
Of course, being a mum and a student, I have often had to cut corners. So you can study the courses in less time than I say above, but it's not necessarily something I'd recommend.
When does your Exploring Psychology course start? If you have time to do a 'short course' (a 10 pointer) beforehand it might help you to get back into studying without completely jumping in at the deep end.
I used to teach S103, 'Discovering Science', which is a required course for most named science degrees, and I could often tell the people who had started off with a short course, as it meant they weren't so shocked by the amount of work when the course got going. And sadly there is quite a high drop-out rate as the courses get tougher.
Sorry if this sounds negative. I still think the OU is a great university and a great way to study, but it's worth knowing what you're letting yourself in for.