{
    "_id" : ObjectId("5ab1119b646e371568c8cf9e"),
    "date" : ISODate("2018-03-20T13:46:30.018Z"),
    "__v" : 0
}

db.getCollection('monitors').aggregate([{
        "$group": {
            "_id": {
                "year": {"$year": "$date"},
                "dayOfYear": {"$dayOfYear": "$date"},
                "interval": {"$subtract": [{"$minute": "$date"}, {"$mod": [{"$minute": "$date"}, 60]}]}
            }, "count": {"$sum": 1}
        }
    }]))