Careful planning, measuring, precutting KO's, or making holes in wall's, installing what can be installed ahead of time, maybe even pre cutting anhy new conductors to be used before ever shutting down, can make it go pretty fast when you are shut down, but any mistakes can also dramatically slow things down.
If what needs moved/replaced is going to take too long there could even be possibility you can disconnect on a Saturday place some sort of temp wiring and do a majority of work during the week and transfer back to permanent wiring the next Saturday.
You have 4 -4 inch conduits and 500 kcmil conductors, but what is the actual loading, might be sized for expansion and true load is well under the ampacity of what is installed - if so any temp bypass may not need to be so large, (may need to temporarily use lesser overcurrent protection also though).