Database
[{userName:"Bob",userActivity:{"hourly":[ISODate("2022-05-09T02:31:12.062Z"),ISODate("2022-05-13T19:37:42.870Z")]}},{userName:"Roy",userActivity:{"hourly":[ISODate("2022-05-09T02:34:22.093Z"),ISODate("2022-05-09T18:32:54.851Z")]}}]
Query
db.collection.aggregate([{$match:{$expr:{$gt:[{$size:{$filter:{input:"$userActivity.hourly",cond:{$gte:["$$this",ISODate("2022-05-13T00:00:00.000Z")]}}}},0]}}}])