People who organize parties are notorious for failing to fulfill duties and responsibilities that of organizers - such as notifying the attendants of important info and/or supplying time/directions to their events or parties.
With that in mind, all you need to do is have self-control and always be polite with them - they are the types of people who are most likely to have a short fuse most of the times, and you do not want to piss them off. So what that entails is you having to be nice to them and simply sending them a text message or calling them again just to remind them about what they had said earlier. That's all. Simple, isn't it? The hardest part is maintaining self-control, because party organizers surely know how to piss many people off with their frequent lack of responsibility and flakiness.
"If you see a difference between where you are and where you want to be... consciously change your thoughts, words, and actions to match your grandest vision." - Anonymous
"What would you do with your life if you had no chance of failure? Start doing it now." - Anonymous