I've had a brief look around on here and have spoken to a few people and have heard mixed reports on these matters so I figured I'd put them on here.

If doing a PhD, how rigid are the 'working hours'. I've heard reports of people getting up late and working late, people working at home and actually not so many reports of 9-5 work. What is it like? I'd be looking at a science but a theoretical based one. As it stands, for my research project in my current degree, we're not required to sign off for 6 hours a week in laboratories, we're allowed to work from home (which suits me well).
My reasons for asking are that something that's more flexible would widen my possible institutions due to commute times and I'm also more productive when not stuck in a 9-5 environment.
I'm also interested in regards to societies and clubs. I'm currently a president of one of my Uni's athletic union clubs and I'd be very interested in investing quite a bit of time in an au club / society while doing a PhD. Is this realistic?

I'm 5 months into my PhD (developmental biology) and I work roughly 9-5 cause thats when I work best. I play for my local rugby club which trains 2 times a week and has games on Sunday. I also share a horse with a friend so I ride three times a week. I asked my supervisor if all this outside activity would affect my PhD and he said at the moment it was fine and he was happy with my progress, but he did say that I might have to rethink things towards the end of my second year and during my third year as that is when he said the work load would probably increase.

As long as you and your supervisor are happy with how you are progressing then I would say that outside activities are great as they help keep the stress level down.