Unclear on the concept

UCLA has been requiring weekly COVID tests of the spit-in-a-tube variety. The tests are available in vending machines accessible with a Bruincard. According to the instructions with each test, it is important to drop the sample in the box next to the vending machine within one hour of gathering it.

However, according to the sign on the box, if the sample isn't put in the box by 11 am, it isn't processed until the next day.

So why is it essential to put the sample in the box within one hour?

I guess this is just one of the mysteries of the pandemic.