Before you can start keeping an eye on how long your Firebase Cloud Functions take to run, you need to make sure everything's set up just right.

First things first, you need to link Firebase Cloud Functions with Google Cloud's Operations Suite (it used to be called Stackdriver). Firebase makes this pretty easy for you.

Google Cloud's Operations Suite is your go-to for monitoring and debugging your Firebase Cloud Functions. Here's how to get it all set up:

Step 1. Head over to your Firebase Console and pick the Project you want to keep tabs on.

Step 2. On the Dashboard, look for and click on "Functions".

Step 3. You should now see a list of your deployed functions. Click on any one of them.

Step 4. You'll see a "Details" tab with general info about your function, and a "Logs" tab.

Step 5. Click on the "Logs" tab.

Step 1. Now that you've got Google Cloud's Operations Suite linked up with your Firebase Cloud Functions, you can use its features to keep an eye on execution time. Head over to the Google Cloud Console.

Step 2. On the Dashboard, select "Monitoring".

Step 3. A new tab will pop up with a list of different monitoring services. Pick "Cloud Functions".

Step 4. This will take you to the Cloud Functions dashboard, where you can see various stats about your functions - including execution time.

Step 5. Click on one of the deployed functions. This will open up a graph interface where you can monitor how long the function takes to run.

Step 6. Make sure the metrics drop-down menu shows "Execution time". If it doesn't, click on the drop-down and select it manually.

Step 7. You'll now see a graph that shows the execution time of the Firebase Cloud Function you're looking at.

Step 8. For more detailed info, click on "View detailed graph". This will let you filter by function execution times and use different chart options.

If you want even more control over monitoring execution time, you can manually log the start and end times of a function.

Step 1. Use console.time('myFunction') right at the beginning of your function.

Step 2. At the end of your function, use console.timeEnd('myFunction').

Step 3. These statements will mark the start and end, and the duration will be automatically computed and logged each time the function runs.

Note: 'myFunction' can be any string identifier you choose to recognize the logs.

This gives you the flexibility to monitor function execution times exactly the way you want. You can then access these logs from the Google Cloud's Operations Suite.