I would be hesitant to rely on a test involving timing the exit of water because the same soil will behave differently depending on whether it is moist or dry, full of roots or not. Not to discount what Thijs has proposed (and by all means whatever works for you is great), just to mention the other variables which may be involved.
There are 2 distinct steps involved in the process: the wetting of the substrate (this part can be very different depending on existing soil moisture) and the passage of water through the substrate (which maybe ideally could be measured distinctly from some starting point of mostly saturated soil). These 2 steps do not necessarily occur separately, rather blend together as the soil begins rewetting and then sheds the extra water that it cannot take up at that moment, and so forth.
At some level it's important to be aware of these steps and monitor how they play out when you water. For example: how much water does a given container take to go from bone dry to fully saturated? You have to do this in a few distinct watering events spaced a few minutes apart, because it is impossible to go from bone dry to fully saturated in one watering, given good drainage. I did this experiment today with a couple of pots because I had to make up insecticide solution in water and needed to know the volume required. Turns out 2 different 10 inch pots (3 gallon size, approx.) absorbed roughly 1.5 liters of water each. (Mixed metric and English units are a way of life here on the border.)
For what it's worth, the amount of water soil can hold is pretty closely related to the amount of organic material in it. The same stuff that we add to improve drainage (ie. the timely exit of excess water from the soil) also ends up reducing the water holding capacity as well. And thus as a general rule the better the drainage, the more often you would have to water to keep needy plants happy.
