Theoretically, you should be able to find the civics you've put at -1 (from here 0 should be sufficient as well unless another global value I saw but didn't track down the value of increases all civics by +1) should have no anarchy time at all after my next commit. You'll have to let me know for sure though.
It works as follows now in my game. I´m not exactly sure if it is what you have intended:
iAnarchyLength = -1: 0 turns of Anarchy (thank you!)
iAnarchyLength = 0: 26 turns of Anarchy
iAnarchyLength = 1: 30 turns of Anarchy
iAnarchyLength = 2: 35 turns of Anarchy
I have observed that changing religions also take 26 turns. Do you have an idea where I could change this in the XML?