I think you just want to write five thirty. No need to put pm or anything else since it is obvious that it would not be in the morning.
You can write 'half past five o'clock' - I've seen 5:30 o'clock once before and I thought it sounded weird. Or just 5:30 pm sounds fine especially on homemade ones. Wow, that is quick timing on the wedding! We are getting married the day after. She's lucky to have your help, if I recall correctly, you are very creative.
THANKS
I think that sounds good and actually is probably easier to read that half past five o'clock. Some might mistake it for five o'clock if they read it quickly, which you know some people do.
Try not to make yourself crazy...as I'm sure you know from your own wedding it will all be beautiful in the end.
