yup, you pretty much have to time it just right... It clicks 3 times, then stops, and then the portal appears for a split second... if you have good reflexes like my lizard rogue, you can do like him and toss a rock over as soon as the portal pops... otherwise, use the clicking sound as a workup.
Hint: afterwards, you can also leave another rock at the pressure plate that triggers the timed portal mechanism and... go stand somewhere else...
