On the free plan, you will get 60 minutes of noise-free audio streams per day. You can get x1.5 free minutes daily if you switch from your personal email address to a work email address. Check this article for more information.
The minutes are calculated based on the presence of the audio stream in Krisp app and if the Remove Noise toggle is turned on for either microphone or speaker.
The Remove Noise toggles keep the last preferred state and do not turn off themselves. This means that if Krisp mic/speaker start being used anywhere, the minutes will be counted. An unintentional use, in this case, can be opening the audio settings of an app where Krisp devices are selected even if there is no ongoing call. The devices are being considered as used at that moment.
The minutes renew each day at 12:00 AM GMT. If you've used all your allowance, you would need to wait till the renewal time to get more minutes or upgrade to the Pro plan to get unlimited minutes.
With the Free plan, you can only be logged in to Krisp on one device at a time. This means that if you log in to the same account on a second device, you will be logged out from the Krisp app on the first device.