Audiences in SharePoint Online are as good as useless, because the audiences are compiled once a week. Unless you exactly know what you’re doing you can give it a try, but waiting a week to get your audiences compiled and afterwards finding out that you forgot one property is not very satisfying.

According to this forum, the compiling will be once a day in the future. So, lets wait for that.

http://community.office365.com/en-us/forums/154/p/966/2953.aspx#2953