In my memmory it takes longer to built an 80/80 infiltrator than 2 months. That's without the having to get enough h/p to be even considered when you have to start over with a new knight.
True, though it doesn't take more than a few months, I assure you. No more than a year guaranteed (if you're not lazy)
I'm sorry, but an infiltrator rarely trains in the academy all the way to 80/80. That is wasteful in the gold department and boring, around 50/50 or 60/60, you train through the actions and deeds of killing militia because it trains both infiltration and swordfight.
A boss infiltrator is in the 90/90 area... 80/80 is just someone who hasn't died yet. Though, great impossible feats can still be commonly accomplished in the 70/70 area.
The Infiltrator class requirements for honour and prestige can be gathered within a month, hunting rouges. Inna war, twice as quickly.