I study at the Birkbeck (undergrad Year 3 now, 3 evenings/9 hours a week) and many of us are part-timers. The extent of our working hours vary from having no job at all up to full time jobs (I'm doing a PT degree, PT work but I know there are some people in our class who do FT/FT and I honestly don't know how they manage).
As for the hours for self-study, I'm not sure if anybody actually does the recommended 2hours per an hour of contact time, I'm quite bad with that and so are those classmates I know but it does get crazy around essay and report writing times and exams. This year has been particularly hard with home study so if you start next year, you may be more motivated to stick with regular study week by week. Hope it helps.