Whopity
As I understand it the limit for pilots effectively means no self administered alcohol. The very small amount allowed covers those individuals whose body produces a small natural amount of alcohol. The maximum limits equate to around a quarter of the normal drink drive limit which in turn is roughly 5 units of alcohol.
The amelioration rate of alcohol is roughly 1 unit per hour (about 1/2 pint of normal stength beer) for a normal sized healthy male but can vary enormously between individuals and as DX Wombat says can vary depending upon physical condition, whether you have eaten or not and what you have eaten.
The problem is that these figures are all very approximate and it is very risky to try and self-assess.