I'd say "It's five thirty p.m." or "It's half past five in the afternoon". I think other members will have different answers, Ediskvaka, so you should wait until you get a few responses to your question.
Both sound a little odd as it's usually pretty clear whether it's morning or afternoon.
More common would be "It"s half past five" or "It's half five". If you want to specify what time, e.g. a train leaves you'd be more likely to say "five thirty p.m" or "seventeen thirty". Usage may vary from one region to another.
I've never heard half past seventeen. I would always say seventeen-thirty for the 24-hour clock. I'd probably say 'half past five' or 'half five' (the latter is BE style only) without 'pm', because usually the context make it clear whether it's early morning or late afternoon. If I need to make it clear, I'd say 'in the afternoon' rather than 'pm'. I might say 'pm' with 'five-thirty' though.