Written in 1508, published far after his death, this is Trithemius well-known astrological history-lesson in the translation of William Lilly (1647). Trithemius starts at the year 0 and writes all the way to the year 6732. Trithemius says what angel rules over which period of 354 years and 4 months and this what is the nature of that period.
FBN also seems to have the (more interesting) Steganographia of Trithemius in three parts, but I don’t know if that is an English translation or not. I need to get it anyway, even though I have the Latin version already.