To enable 'Time taken' for temperature, simply tap the gear icon in the 'Temp’ / ‘Temp two' card on your data screen (note that you may have renamed these temps).
Then in your temp settings, scroll down a bit and you’ll see the option to enable ‘Time taken'.
After this you can also check that 'Time taken' is set to display on your chart by tapping the three dots icon at the top of your chart screen then the gear icon.
Happy charting!