Firestore moving to timestamps in Firebase functions

You are still receiving JS Date instead of Firestore Timestamp due to a bug... now fixed in Firebase Functions v2.0.2. See: https://github.com/firebase/firebase-functions/releases/tag/v2.0.2.

For initialisation I've used admin.firestore().settings({timestampsInSnapshots: true}) as specified in warning message, so the warning has disappeared.

When you add a date to a Document, or use as a query parameter, you can use the normal JS Date object.

add below 2nd line code in your index.js firebase functions file

admin.initializeApp(functions.config().firebase);  
admin.firestore().settings( { timestampsInSnapshots: true })