Comment # 2 on bug 1205465 from Ulrich Windl

The confusing part is that some packages come with their manual page, while
others do not.  My guess was that the pages of the minimal base system are
included in the manual pages package, while any additional man pages come with
the corresponding packages.
From a maintenance point-of-view that also makes sense, because you want to
read a manual page that corresponds to the program being installed.
So general expectation was that if you find a manual page for a program, that
program should also exist.  I also use "man -k keyword" frequently to find out
which suitable programs do exist in the system.
Finally as systemd timers did replace "at", it would make sense to move the at
manual page to the corresponding package that ships the actual at command IMHO.