It was impossible for Ves and Jovy to properly design a complete juggernaut mech in less than 4 hours.
They were working so far outside of their comfort zone that they couldn't directly reuse any of their old design solutions.
Juggernauts were just too different. The 300-meter long mechanical monstrosity possessed a volume that was comparable to a starship.
The quantity of parts that made up a juggernaut was an order of magnitude greater than that of a conventional mech at the very least!
While Ves and Jovy were able to skip a lot of additional work by multiplying the size of parts by a lot, they weren't able to apply this approach on every single part.
There were still a lot of functions that couldn't be solved in this manner. The pair of Seniors had to tackle a lot of design problems the hard way.