In most cases, it will take approximately 30 seconds for the NC° Thermometer Gen2 to finish measuring.
To make sure that you are measuring correctly and that your thermometer is working as it should, we always recommend completing the Measuring training in the app when you get started with Natural Cycles, which you can find under the top menu > My device > Troubleshooting and help.
We recommend reading the instructions listed in this article before completing the Measuring training.