From the band's facebook page:
The album title was inspired by a simple chronological fact. “This will be released in mid-January 2020,” says Portnoy. “That means it will be one of the first releases in what is a new decade.
Ummm, if I am not mistaken this decade started on January 1st, 2011 and will end on December 31st, 2020. Correct? So the new decade will start on January 1st, 2021 not 2020 as MP said.
A decade is just a period of 10 years. You can pick a decade with any start or end date. A new decade started right this second.
Since we call the first year of the current calendar year 1 A.C., then yes technically the decade that started at the beginning of year 1 only ended at the end of year 10. And the decade immediately following that started year 11 and ended year 20, so we could follow that through 21-30, 31-40... 2001-2010, 2011-2020. But there's no reason we're constrained to do that. When people refer to a decade, 90% of the time they refer to the decade that shares a common digit in the 10s (e.g. the '80s). 2000-2009 is a decade just as much as 2001-2010 is a decade, and it happens to be one that's much more easy to refer to as a group and so that's what people do. The '80s, '90s, 2000s, 2010s and 2020s are a much more relevant and useful way to arbitrarily mark the start and end of decades than going back to a quirk of the calendar and following it through 2000 years to mark your decades in ways that are more awkward to describe and don't match what most people are using.
To be honest I sort of lost track of MP's activities and I wasn't sure how quickly there would be a follow up Sons of Apollo album. I never got into the first album much (and the drama around the project made it a bit of a chore to follow) but I liked it some and it at least had potential, so will be cautiously hopeful for this.