Just in case anyone is confused:

In Individual Levels you MUST have a rating screen at the end of the mission to confirm in-game time. Any resets before the successful run will not be considered in IGT calculation. No saves/ loads allowed.

For full-game runs resets are allowed only if you have the in-game timer HUD on. Add any time that elapsed in a level when you reset (based on what the timer HUD says when you reset) to the total IGT. Rating screens still required. No saves/ loads allowed.