Here's a blog post we've just written on this topic. Hope you find it useful!
"“How often should I post?”
As a page manager, this is a question I struggle with daily.
Here are a couple of things to keep in mind when deciding how often to post:
1. A post’s life is very short:
A post will reach 75% of the total number of people it will be shown to within 2 hours! And about 90% within 4-5 hours."
Read more here:
http://orangetwig.com/blog/how-often-to-post-on-facebook?ref=teamHow often do you post on your page?