Stability of connection might be a more preferable metric, particularly in noisy urban environments. A theory I agree with for that is to choose the non DFS band(s) (depending on desired channel width and included device compatibility) to prevent the network from hopping around at the cost of slowing down when the noise floor (other broadcasters) increase.

Is there a way to determine how often a DFS band will be interrupted in your area?

Yes. Testing it. :) How else would you find out? It depends on so many factors. Nearby radars, placement inside the home, sensitivity etc.

The only thing you can do in advance is check for radar transmitters in the 5-6Ghz range nearby. Be aware that these are usually in a pretty specific frequency, affecting only a few channels.

How do you check for it? I have UniFi equipment- is there something built in that can monitor it for me? How long a test do you need? Can/will it change over time?

If you're using a DFS frequency and the device notices it needs to change frequency because a primary user transmits the Unifi console will log DFS events in the notification area. It won't emit any notifications if you're not using a DFS channel.