Job advertised as full time but also says part time/job share, when to bring this up?

[HarryPottersMagicWand]

I have an interview in a couple of weeks, civil service. It was advertised as full time 37 hours. But underneath it said part time/job share. I phoned up to ask for clarification and was told if it said that then they will accept part time hours, as this is what I want. Due to health issues, I don't want anything more than 16 hours a week.

When do I bring this up (the hours I actually want)? Do I mention it at interview , would this influence their decision? Or if and when I was offered the position? If I waited until then, and then informed them I only wanted part time, could this mean they could retract the offer?

I applied for a job which was advertised as full time or part time. I stated on my application that I was interested in part time hours. At my interview, I was asked about this so I said I wanted to work part time (due to wanting to pick up my DC from school). I got the job. Personally I think it's better to be up front about it.

That was my thinking. I wouldn't want them to think they were about to employ someone into a full time role and then for me to say I want part time, although I know someone who did this successfully.