Quote from AUTUMNTWILIGHT »How does time work on different planes anyway? Are we just going with 24 hours everywhere and 365 days a year to keep things simple. You could say the timelines are desynched right now and that is the twist.
Orbital rotations are technically different on different planes, but a "Year", as mentioned in the story these days, is approximately the same unit of measure everywhere. We didn't used to think so, but Teysa's modern age of 112 only works if she was born around 9965 Z.C. like is said in Guildpact, which would put the events of the original Ravnica block just a few years pre-Mending and still add up to the modern day.
So a "year" when mentioned in-story is the same unit of measure everywhere (otherwise everyone in-universe would have to constantly be doing math), even thought technically planes have different solar cycles. I know it hurts, but it's the easiest way to track a multiverse-spanning narrative. The whole different years mean different things only worked when you never saw much cross-pollination.