Want to have better reach on your posts? Don't schedule for on the hour as that's usually when every other scheduler auto-schedules posts and FB can often be flooded.
Schedule for off the hour and you'll have much better reach!
Also FB research shows us that Facebook posts get half their reach within 30 minutes of being published so as easy as it would be to just say post at this exact time for the best reach it's not quite that easy. You need to do what's best for your specific party.
Is your host mostly inviting workers who are likely to be busy from 9-5? Then maybe aim those posts for lunch or in the evening when they're off. Moms who are kid free from 8-3? It would be best to take advantage of that window. In order to know the best time to post for each particular party you need to consider your audience, students? Stay at home moms? Business individuals? Late night performers? Tailor each party for the audience you're expecting and don't just assume what works for one will work for all.