So I'm trying out some full runs, but want to understand the calculation for IGT, I get adding them up and multiplying by .75, but if you have to reload a save I don't understand how that's calculated. Is that what the 10 second penalty for "delay of game" is? Or do you manually have to go back and see when the save was loaded and add the amount of IGT to the level you had to reload?

Latter. And it's 0.725. Delay of game is if you pause the game without loading or unnecessary slow to start the next mission.