I think you're fundamentally misunderstanding things. When I've worked on systems like the one EliRivers is describing, you don't have a choice between hacking

I think you're fundamentally misunderstanding things. When I've worked on systems like the one EliRivers is describing, you don't have a choice between hacking something together in X time or doing it correctly in 20X time. You have a choice between doing it in 20X time and not doing it at all. If it's a part of the system you haven't touched before, it simply isn't possible to make changes without taking the time to understand what it's currently doing first. The only part of the process that's optional and could theoretically be skipped is turning your notes into documentation consumable by others, but that's a pretty small portion of the time spent.