hey stephen,
you can set this up at your easysocial backend -> profile types -> then click on the user type you want to modify. from here select the "access" tab and there select "conversations" -> Daily Send Limit

if you don't see this setting there go to your easysocial backend -> access -> and click on "discover".
after easysocial has found the rules go back to the page mentioned above and then the limit options should show up.

hope that helps and have a nice day