Short answer: Submit your run with an approximate time. Mods retime every run with a frame counter while verifying the run.
Long answer: If you are submitting a single map run, just put your time as time without loads, and leave the time with loads blank. Time starts when you move and ends when the text box comes up. If you are submitting a multi-map run, it's a little weird. Time with loads is just time from your first movement on the first map to the time the end text box appears on the last map. Time without loads removes the time that you are on the main menu between maps and the load into the new map. Overall, it is nice when runners are at least able to give us pretty precise times. But as long as you get the right category and put down a decent approximation, we'll get you situated.
New Category added to the board, "All Categories".
You can find it on the Main Board under "Misc."