I cant say for sure but I played a female character and when one guy finally agreed to marry my character I went back after a few days and he said something about not being able to wait so lets just get married in any hall. I followed him around and waited till he was in a castle or town (cant remember if it matters) and then went inside and talked to him and a few dialog options later we were married (not that much changed).
My best guess would be to wait for a feast and lots of lords and ladies gather in one spot for those.