Once you have made your run over the existing record and come to Impound, you will stay there until a return run is called for (always the next morning with possibility of the same day if it is the last day).
If you leave impound with the vehicle; your qualifying run will be negated and you will need to start the process again.
The next morning you will make a return run, when it is averaged with the previous qualifying run, and if it averages over the existing record you will have said record after it is certified. Also the same relative mile will be used and only the highest average will be used, you do not get to pick if 2 or 3 are over the record.
If you choose to raise it, you must now qualify on the higher "new" record which has been set. You will need to return to Impound if you are successful in doing it and run the following day.
Do not try to over think this process. Good Luck