Temperature too slow to update

This is normal, it takes some time for the sensor to ajust to the current temperature. It's the same with all Garmin (and non Garmin) devices. My Fenix takes about 10 to 15 minutes to ajust, even when I use my Tempé sensor. If u want to have the temperature correct at the beginning of your ride u need to get your device outside about 10min before your ride.

Yeah, I'll second the moderator. This is true for any thermometer. It's got to dissipate all the thermal energy stored around it. You could keep the 520 outside so it's ready to go. That's a nice short commute, be happy! :^)

I am sorry to disagree, but this is not a hardware problem. There is no temperature latency of the unit - it is small and light, and cools down almost immediately.
I have done the experiment, taking it out from 22°C to the -10°C outside, for 5 minutes. It shows 17°C. Then I wrap it in a blanket, and leave it inside, at 22°C, for another 5 minutes. Then it shows 12°C. So the reading continue to drop while the unit temperature stay relatively the same.
Another experiment - taking the unit out from 22°C to 12°C, for 5 minutes. The temperature readings drop exactly the same, 17°C. If the unit was just slowly dissipating heat, it would cool down slowly. But no, the temperature readings go down with the same speed.
Obviously the unit is extremely slow to update the readings.
I understand the idea behind hysteresis and slow update. But Garmin have overdid it, by lot.
My smartphone has a temperature sensor, and it updates much faster. Even if the smartphone is much heavier.

And no, 30 min ride is not a short commute. I need the temperature to adjust my clothing. 15 minutes into the ride, is way too late, I am already sweating or freezing.