Teaching
Ves already possessed enough skills and experience to fabricate a flawless mech in six days. In order to compress the fabrication time to four days, he had to drop his excessive caution. He stopped double-checking and triple-checking most of his routine work and only slowed down when he reached a difficult phase.
His previous experience along with his ample preparations smoothed out his efforts to speed up his work. He already formulated standard set of responses to any problems he'd likely be facing.
"Watch carefully now." Ves instructed his attentive employee. "The fabrication of mech components is usually the most challenging portion of the fabrication process. The Mark Antony Mark II and the Caesar Augustus it's based upon are anomalies because their assembly phases are hellishly difficult. That does not reduce the difficulty of printing the parts."