It depends on how much micro-management you want to do, because at high or max speed nothing takes particularly long no matter what your 'goals' are. You'd get through a full game in less than a day at high speeds. It's good to have these skills if you want to play multi-player.
My games can take a week full time or more ... I pay attention to training generals in specific traits, maximising experience of units by sending volunteers, developing my army and templates before war to maximise pre-war experience... I play mostly historical runs... I pause to plan, mapping out production, the timing of focuses and spy missions etc for maximum effect, I control battles carefully rather than using too many battle lines (which lead to pure attrition warfare).
I played a lot of HoI2 but almost no HoI3... for me the time it takes for a HoI2 game vs HoI4 is roughly same.