Dilution vs. Substitution for a pre-employment test

[Burnt Toast]

Another wrinkle in the plan... For the test, I have to go into the office (about a half hour from where I live), fill out some paperwork, then drive down the street to get the test. All in all probably an hour or so from leaving my house to the test. Is substitution still an option?

The answer to that is yes.
Consider picking up a handwarmer pack or two (at your local sporting/camping goods store)....or you can use your vehicle heater (with the switch on floor duct mode) to keep the sample warm.