Why does the COVID-19 Test Home Collection Kit sample need to be mailed back on the same day as when it’s collected?

Shipping the sample back on the same day as when it is collected will ensure that the sample is within the stability window by the time that it arrives at the lab. Kits should be dropped in a UPS drop box or picked up via a regularly scheduled UPS pickup on weekdays only and before the last pickup time on Friday. If the sample is dropped off after the last pickup time on Friday, there is a risk that it will sit in the drop box all weekend, and could expire before the lab is able to process it.