Suggestion
Facilities offering speed up for rich Sam?
For example:
Looking at times seems we are paying for one workman, plus up to two allies can assist. If one workman costs X Euro (eg. 400 Euro, heh, what, a shortage of skilled workforce in Reiker city). Then can allow us to hire one more for this X Euro in addition to the upgrade price. (eg. the first lvl can cost 600+400=1000 Euro when want to hire two)
Using the current (v25) time numbers:
24h <- 1 workman
12h <- [2 workmen] OR [1 workman + 1 ally]
8h <- [1 workman + 2 allies] OR [2 workmen + 1 ally]
6h <- [2 workmen + 2 allies]