I happened to come across the Alto's time handling code [1] while looking for something else. The Alto counts seconds since Jan 1, 1901 and the time can run until 2036 since it uses a 32-bit value. (Unix time in comparison runs from 1970 to 2038; it runs half as long because it loses a bit by using a signed value.)
The point of this is the Alto can handle dates until 2036, but will run into problems two years before Unix self-destructs in 2038.
Good to see they at least thought some reasonable amount of time into the future; in contrast, the Apple Lisa, released 10 years after the Alto and a few years after the IBM PC, had an RTC that only went to 1995:
(Apart from this shortsightedness, the rest of the Lisa's design is also... interesting. Proprietary custom ICs, a pretty much locked-down user-is-an-idiot GUI, and complete separation between users and developers. It failed then, but unfortunately the same strategy is now considered the norm 30 years later...)
The point of this is the Alto can handle dates until 2036, but will run into problems two years before Unix self-destructs in 2038.
[1] http://xeroxalto.computerhistory.org/Indigo/AltoSource/TIMES...