Predicting when Zwift updates will drop is something that I have been doing for months. Over the months, I have gotten pretty good at it. Here is everything that I look at to figure it out.
The Zwift Updates are typically released on the second or third week of the month. So anywhere from ~ 8th-20th. They are released monthly, and release anywhere from 9 AM PDT – 11 AM PDT. This is because this is the time range when the most Zwift employees are working.
The Zwift Forums are where the update release notes are released. It is also where people from ZHQ post updates on bugs. These posts typically include the week when the update is scheduled to release.
Also, keep an eye out for these next couple of weeks. Zwift is supposedly releasing some new stuff!