Welll... one way is to do something like:
$ coproc sleep 100
$ sleep 20
$ kill -9 $COPROC_PID
The "sleep 100" is the command to be timed. The "sleep 20" is the time to wait for it before aborting it.
The "kill -9 $COPROC_PID" aborts the coprocess pid (which is the "sleep 100" line).
If the timed command terminates before the kill command then the kill will get "no such process" error.
You can lookup the coproc and is assocated PID handling in the manpage on bash.