If I remember correctly, the procedure was to prepare a food sample, put it in a temperature-controlled environment for 24 hours, and next day see if something grew there or not. If it did, the food was contaminated.

You could try shortening the time to 6 or 12 hours, but then

1) if something grew then the food was contaminated, but if it didn't, how can you be sure it is good or you just didn't wait enough? You would get a lot of false negatives.

2) the lab followed a normal 8 hours a day schedule, so nobody would be there to analize the results. You would not gain anything.