The cure of concrete and mortar are 2 different things, and refractory mortar is another totally different thing. They all do share one characteristic: The rate of cure is not linear. For example, an adequately hydrated concrete will cure to 70% of final strength in 24 hours, 90% in one week, and 98 percent in a month. That is portland cement based concrete, but calcium silicate mortars perform at even faster cure rates.
The most obvious way to prevent excess moisture in the oven is not to introduce it. Dipping the bricks, using a wet mortar, cleaning the laid face with water, not covering the oven, etc are all things that are not required, BUT are very common for someone building an oven in their yard. That is why those instructions are all good and valuable, but as he says, "to be safe". He is in the business and has to be safe when instructing unknown people with various skill levels.
In construction (this is why I asked you), normal practice is to place concrete and strip the forms the next day, with CMU being laid the same day as an example of how normal construction is done as opposed to how it may be done by DIYers.