Today was the launch day of the new "Elemental Evil" module. I haven't looked at any of the new content yet, but I logged all three of my characters to invoke, as I usually do. There I learned that invocations have been changed: it used to be that you received the biggest benefit from invoking once per day, after which you could repeat the ritual once an hour while experiencing high diminishing returns. By the third hour it was nearly useless.
Under the new system you can invoke once every fifteen minutes, but you only receive a much smaller reward the first time. To maximise your Astral Diamond gains from invoking you basically have to do so once every fifteen minutes for one and a half hours. (EDIT: I initially misread the timers, actually the time increases after each invoke, making for a total of four hours.)
That kind of sucks for those of us who have been "playing without actually playing" for prolonged periods of time, but it rewards people who spend time in game every day beyond a five minute login. Can't say I can blame Perfect World for this change.