Depends on the motor and how good are you are wiring.
The questions you are asking ultimately rely on the person doing the works abilities, amount of time researching, and time planning in advance.
If I am working with a carbed motor, I can have that wired in less than an hour to get it running and all gauges working.
If I need to pin out a harness for an LS style motor and mate it to a stock 4.0 wiring to get the two factory systems to talk with each other, or at least operate independently but simultaneously, I would could spend up to 10 hours. Most of which is reading FSM and chasing wires to pins.
Personally for me, if I am swapping a motor for offroad use, I will not remove a EFI motor to swap in a carb with the amount of off camber and steep hill climbs in my area. I can save a metric crap ton of time by buying a pre-made harness, but it will cost me anywhere from $500-1000 (depending on motor and options and ECM flash).
Another option is to go with propane LPG which you basically swap the carb for a propane hat.
