Detected an object of type "Timestamp" that doesn't match the expected instance

Now I get it why it throws an error. Because I import Firestore object separately, whereas I should just use Firestore object from Firebase Admin SDK.

What I changed:

1. remove "@google-cloud/firestore" dependency from package.json

2. Use admin.firestore.Timestamp object.

index.ts

async someFunction() {
   let col = firestore.collection("mycollection");
   let now = admin.firestore.Timestamp.now();
   let twentyMinsAgo = admin.firestore.Timestamp.fromMillis(now.toMillis() - (1200 * 1000));

   col.where('LastEdited', '>=', twentyMinsAgo) //Now ok
      .get()
}