Database
[{"createdAt":{"$date":"2020-09-29T01:52:10.199Z"},"updatedAt":{"$date":"2020-09-29T02:55:10.199Z"}}]
Query
db.collection.aggregate([{$project:{dateDifference:{"$divide":[{$abs:{$subtract:["$createdAt","$updatedAt"]}},3600000]}}}])