On second thought...

"Often people ask: How long should
I meditate? And when?... The point is
not how long you meditate; the point
is whether the practise actually brings
you to a certain state of mindfulness
and presence, where you are a little
open and able to connect with your
heart essence. Five minutes of wakeful
sitting practise is of far greater value
than twenty minutes of dozing!"

--Sogyal Rinpoche