The first mention of it came out in early March 2016 on vlog 9, when Sparkles* stated he was working on new ideas on the third album, even before Modern Synthesis was released. He also stated then that it will come out closer to Modern Synthesis than Modern Synthesis was to All The Lights In The Sky.
Then next nod to it was mentioned in early January 2017 on vlog 31, when Sparkles* confirmed that they were writing a new Area 11 Album. He also mentioned in a reddit comment that one of his New Year's Resolutions was to complete the Album, giving it a 2017 release date.
Some content was actually released late April (although the footage was recorded early March) on vlog 39. Sparkles* showed about 2 seconds of one demo, recorded by a microphone through headphones at max volume, so the quality was not good. He talked about he was coordinating with the band on these demos online, but once he got back to London, they would begin working on it full force.
On June 8, 2017, an interview with Area 11 was released (source), where they talked a bit about Album 3. Kogie responded, when asked about if the new album could be R.E.M. inspired "No, no, no. Not “could be”. It is". They also stated that they're at the stage of "collating and whittling down our demos". They did state though that "We’re not setting ourselves any hard deadlines". Sparkles* also mentioned he wanted to get a producer on the new album.