This is a two part answer. Liquid extracts are completely bioavailable. The body does not have to break down liquid in any way prior to entering the small intestines which is the next step after the stomach in the digestive process. Some producers sell powdered herbs that are encapsulated in gel caps or gelatin capsules. Powdered herb has cellulose, our body needs to break down the cellulose and process that herb material into an extract via the digestive juices. This is a very inefficient and frankly ineffective way of getting the benefit of the herb. In combination with alcohol, which is absorbed nearly immediately into the system, the longer the herb takes to break down, the more the risk of not absorbing the extract increases. This makes liquid extracts the fastest and most effective delivery system.
There are a few factors that determine this. It depends on the state of the body, what the condition is, its severity and how long the condition has been affecting one's life.
It depends on whether the person is complimenting the herbal regimen with vitamins, minerals and a reasonably healthy diet while eliminating the antagonist. One example would be if someone is trying to rejuvenate one’s liver with a liver herb but continues to consume alcohol excessively and/or consistently eat sugar the process of seeing positive results can take much longer/if at all to see the positive results they are looking for. But on the other hand, if one removes the antagonist, supplements appropriately and adopts a healthy regimen, benefits can be noticed within a week and in some cases as early as a day. Again this all depends on the individual and their respective situation combined with one’s own will to make more constructive choices.
Liquid herbal extracts made with alcohol can last indefinitely as long as they are stored in a cool, dark and dry environment. (We still have tinctures from 2007 that have not changed in taste, color or efficacy.)