27.0.60; Asymmetry between (days-to-time) and (time-to-days)

[Kevin Liu]

The asymmetry between (days-to-time) and (time-to-days) is quite surprising:

(format-time-string "%Y" (days-to-time (time-to-days (current-time))))
"3989"

One could work around this by using (time-to-number-of-days) which uses
the epoch time like (days-to-time), but that itself is awkwardly
asymmetric as it returns a float, as well as the asymmetric naming.

It's probably unrealistic that any existing behavior be changed, but it
would at least be nice to have a builtin function that is the inverse of
(time-to-days).  Org-mode, for example, seems to use the Gregorian
convention of (time-to-days) throughout, and to convert a (org-today) to
a time requires this mess:

(format-time-string "%Y" (days-to-time (- (org-today) 719162)))
"2020"