"tech in a can" ? Like the General said in the movie War Games, "I'd pee on a spark plug if I thought it would help." As far as a specific time, probably only as it relates to when the sun gets high in the sky. It's been cool and cloudy today so of course it's working.
I spend my winters in southern Arizona and California so I encounter border patrol stations frequently. After a teardrop rally this past February I was about 10th in line going thru a checkpoint. There were 4 Border Patrol officers & 1 German Shepard drug dog. This particular day it seemed to be a pretty fast process with the officers asking where you had been, a quick glance inside and then waving people thru. Until it was my turn...the officer with the sniffer dog puts his hand up to stop and they all approach my car. Yikes, was this going to be a full on inspection? Do I have anything in here that might be considered contraband? But no, he was considering buying a T@B and wanted his buddies to see it and how did I like mine! Big exhale on my part!