I would recommend tasting the beer after a week using a wine thief. The small barrels have a very high surface area to volume ratio and do not need long aging. I have used two rum barrels and the first use of a new barrel for me was between 7 and 10 days. Bigger beers can handle a bit more time. The second use of the barrel will need to be about twice as long and I have been able to reuse 3 or 4 times before turning them into sour barrels. I put a bottle of rum in them and rotate the barrel every few days in between beers to keep the barrel from drying out.