[ksh93u+m] alarm timer function

In ksh93u+ I'm using the built-in 'alarm' timer command.

$ alarm --man
Usage: alarm [-r] [varname seconds]

(The original 'alarm' feature may have been experimental
and not documented well, but it was nonetheless useful.)

Just noticed in ksh93u+m that the 'alarm' timer command
doesn't seem to be available; I now get errors like
  "alarm: not found"
and
  timer.alarm: invalid discipline function

Is there some substitute in ksh93u+m that will replace
that function from the original ksh? (Or something else
to do to get it working?) Or has that feature just been
abandoned in the "u+m" branch?

Janis