Database
[{"key":1,"createdAt":ISODate("2022-01-01T05:10:10Z")},{"key":2,"createdAt":ISODate("2022-05-01T15:10:10Z")},{"key":3,"createdAt":ISODate("2022-02-05T05:10:10Z")},{"key":4,"createdAt":ISODate("2022-03-01T04:10:10Z")},{"key":5,"createdAt":ISODate("2022-04-01T10:10:10Z")}]
Query
db.collection.aggregate([{"$match":{"$expr":{"$eq":[{"$hour":"$createdAt"},15]}}}])