The time זי"ת ז"ך is after one Shmita of Yovel פ"ה. It is also two Shmita periods into the current Machzor Gadol, in its year Samech, right in the middle of its כ"ח years.
Now, this Machzor Gadol, the appointed time for the restoration of Israel's כח, is number פ"ה since 3417, which was very likely the first year of the first Machzor.
ואשים דברי בפיך ובצל ידי כסיתיך לנטע שמים וליסד ארץ ולאמר לציון עמי אתה
צו