Viewing metrics in the console
You can view your functions with their execution counts and median run times in the Firebase console.
If you notice variability in execution times for a given function, keep in mind that that "cold start" executions may take longer. When a Cloud Functions instance is already running and ready to respond when a function is triggered, execution times are faster than in cases where a new instance must be started to run the function.
More detailed information on your functions can be found in the Cloud Platform Console.