The basic outlines for the new Cutter Hulls were done quite quickly, and the work had begun before Max even had time to get all of the crews arranged to start training on the new systems.
These ships would use a translated version of the navigation system on Terminus, which was of a higher quality and resolution than the ones in most of the vessels available to the Reavers, so there would be some adjustment time needed before they would be ready to actually take it into space.
Then there was the crew who actually had to maintain and repair these vessels, assuming that the theoretical numbers held true and they didn't discover any flaws during initial testing that would require another round of extensive overhauls.