Timeout doesnt work in sentinel

[Järneström Jonas]

In GNU Emacs 20.7.1 (sparc-sun-solaris2.8, X toolkit)
 of Tue Jan 16 2001 on sunray8.era-a.ericsson.se
configured using `configure  --prefix=/usr/bag/emacs/20.7 
--datadir=/usr/bag/emacs/share'

In a process sentinel I have a chunk like this which never timeouts:
  (setq result   
        (y-or-n-p-with-timeout 
        (format "Update %s to %s ? " old-label new-rev) 
        cs-auto-update-query-timeout 'timeout))

While y-or-n-p-with-timeout is waiting, there are other subprocesses
exiting waiting to run their sentinels. Is it this that creates the
problem or can't I use timers in a sentinel at all?

Would it help to write my own version of y-or-n-p-with-timeout
with a sit-for or sleep-for squeezed in somewhere?