I haven't done an access course, but have done an EPQ around A-levels. I think it depends how long you're planning on giving yourself to complete it, from start idea to presentation. I did mine in about 9 months, but that was nothing like flat out work, it was small amounts when I felt like it really. SO I would say that it isn't too time consuming, but then again I have to say I don't think that it helped my undergrad application, it was related to the course and none of the universities mentioned it in offers. But I found doing mine quite enjoyable, as it was a subject I was genuinely interested in, even if it didn't actually help my application. Hope that gives you something to think about.