RGM rotation

Hey all! I just got to summoner level 10 yesterday and it said I unlocked RGM's. I looked around online and found that all the meaningful information about them is from around 2 years ago, so I wanted to ask here -- is there a set or implied schedule? I know Riot's not doing them every patch anymore, nor every weekend, but should I expect them every month? A few times a year? I'd just like to know what to hope/plan for so my expectations aren't unrealistic. Thanks for any responses, especially official ones. [slayer-jinx-catface]