The seven rhythms of SYNC correlate to an annual cycle of Christian and Jewish holidays. In this cycle, the story starts on January 1st with the creation of the world and ends on December 31st looking forward to Christ's return. In between, some holidays like Easter have their familiar meanings and some like Ash Wednesday are given new meanings.
The site menu item marked "Guide" is for one of the rhythms in the cycle. That link changes each time a SYNC rhythm changes on a certain season-opening holiday. The Bible reading lists follow this cycle, and the "annual cycle" option for using the Jubilee Cards also follows it.
To use the cards in SYNC with this cycle instead of the 50-day cycle printed on the cards, choose the seven cards that fit each rhythm. Go through those cards, one per day, as many times as fit into the season length described in the list above.
For example, in 2019 the season for the Vision Rhythm was 38 days long. In that case, you would go through the set of seven Vision cards 5 times (5 x 7 = 35) and use the first three cards again on the 36th-38th days.