There is no simple answer to this question as the degree of purity (or contamination) of YOUR alcohol is unknown. If it's very clean, the carbon will filter lots before it is saturated but if your alcohol is relatively dirty, the carbon will become saturated much sooner.
We recommend that when you filter a batch of alcohol, you do NOT collect all of the filtrate in one large container.
It is preferable to collect the filtrate in sequentially-numbered one-liter pop bottles and, since the first one filled will contain alcohol that passed through new carbon, it must be as good as it gets. Keep this bottle as a control for all future comparisons.
When you've done your filtration, compare the odor and taste of the contents of bottle one with bottle two, then bottle three, bottle four etc, etc until you notice a drop-off in quality.
Everything collected before that point is clean but everything thereafter needs re-filtering through fresh carbon.
This will give you a very good idea of how much alcohol you can clean up with a pack of carbon.