Meditation and the hourglass or egg timer

I call them egg timers but they were based on what we originally called hourglasses; delicate glass bowls with a pinched waist, sand which could pass from the top to the bottom through the little waist.   Once the sand is in one bowl the other one is empty so if you want a perfect egg you use your egg timer to time it.  See the egg below and imagine how long that would take to boil!  The empty side of the egg timer is a great analogy for meditation and emptiness.  The recommended time to meditate is half an hour and the empty glass bowl is what the mind is aiming for.  Once the bowl is empty, it is easy to realise that the space inside the bowl is the same as the vast empty space outside.  But what might we mean by empty? don't we just mean absence of anything so perhaps that emptiness is just a fullness, a totality.