This Maxim tells us that when we act we should act quickly. This does not mean we should act without planning but rather that we need to exercise our minds in order to be able to act in a timely fashion. If we fail to act when we should it then we might as well not act at all. This is reflected in the old saying “strike while the iron is hot”. If we do not act when we should then we often miss opportunities that we would otherwise have.
This Maxim is closely related to other Maxims such as “Know your opportunity” and “Act when you know”. Together with them it states that when we see an opportunity and know what to do that we should DO what we know we need to do. This does not mean to act rashly, but to act in the proper time for the things we need to do. This is the part that is the most difficult as it is sometimes difficult to actually know when the proper time is until you are looking at it in hindsight. That is why we need to look for opportunities to put plans we have already made into motion and then do so.