Mel,
There is always that chance, especially these days when the PO is getting rid of so many offices, postmasters, and carriers. However, there are still may at the PO that take their jobs seriously and perform as they should. If it is just marked Priority with no note of what's inside, the packages can get curtailed for several days if the parcel load is heavy. I was a rural carrier for 8+ years, and I always took charge of the chickens and eggs that came into our office, and would call the customer, go off route, and deliver them first if they couldn't come in. Hang on to your hats folks, because they are making MAJOR cuts in the postal system, and this is going to get MUCH WORSE in the very near future!