This should have been covered in your training, but perhaps the trainer made a mistake. It happens; none of us is perfect.
If you receive the pyx with the Eucharist directly after Mass --say it was a 10 o’clock Mass, over at 10:50, and you receive the pyx at 10:55, and the person to receive the Eucharist lives about 25 miles away, half of it on a dirt road, and you have a reliable but older ‘clunker car’, and it is mud season, it is going to take longer (as it most likely would in winter as well) to get out to the person’s home than it would take in summer. So let’s assume that, in clear dry weather with the roads in decent shape that it would take you about 40 minutes to get there. Well then, you have pretty much 40 minutes, give or take say 10 minutes (if you need gas for the car and couldn’t get to the pump before Mass, for example). As others mentioned, you don’t take the pyx at 10:50 and then go out to lunch, or run errands, do the grocery shopping, etc. before heading off to bring the Eucharist to the person.
at the same time, if it is foul weather, you don’t start to think you’ve gone over the limit and had things ‘expire’ if it takes even double the usual time to get to the house SAFELY.
Common sense. You have a blessed duty to perform, you do so as quickly, carefully, and safely as you can. . .every time.