Question about 2dsphere as compounded index

Question

I have a collection with geospatial data (2dsphere) and timestamps (date) which I need to query based on location (i.e. geospatial) and time (i.e. date).

I have created a compound index with geospatial and time as indicies. However when I perform the query (i.e. based on location & time) the queryplanner says it does a COLLSCAN.

Also, when I add an index with only time it uses that index (ie. IXSCAN with the timestamp index).

I'm a bit confused, I have read that you should be able to use 2dsphere and timestamp as a compounded index for fast finds based on location and time (e.g. MongoDB Indexing: Multiple single-field vs single compound?).

So I guess my question is whether it is possible to use 2dsphere as a compounded index? Does a 2dsphere index behave the same as other index types (i.e. ints, dates etc) or are there any big differences? For example, assume that we have the indicies "timestamp", "geospatial" (in that index order), Can I query only based on timestamp (since it is the first index)?

Link to the docs about 2dsphere: https://docs.mongodb.com/manual/core/2dsphere/.

Thanks in advance.

Example data:

{
    "_id" : ObjectId("5e300c9673f256100d5ca0b2"),
    "geometry" : {
        "type" : "Point",
        "coordinates" : [
            18.2,
            59.8
        ]
    },
    "properties" : {
        "@timestamp" : ISODate("2019-01-01T12:01:00.158Z")
    }
}
{
    "_id" : ObjectId("5e300c9673f256100d5ca0b3"),
    "geometry" : {
        "type" : "Point",
        "coordinates" : [
            12.3,
            52.4
        ]
    },
    "properties" : {
        "@timestamp" : ISODate("2019-01-01T12:10:00.158Z")
    }
}
{
    "_id" : ObjectId("5e300c9673f256100d5ca0b4"),
    "geometry" : {
        "type" : "Point",
        "coordinates" : [
            28.8,
            50.2
        ]
    },
    "properties" : {
        "@timestamp" : ISODate("2019-01-01T12:50:00.158Z")
    }
}
{
    "_id" : ObjectId("5e300c9673f256100d5ca0b5"),
    "geometry" : {
        "type" : "Point",
        "coordinates" : [
            28.8,
            50.2
        ]
    },
    "properties" : {
        "@timestamp" : ISODate("2019-01-01T13:50:00.158Z")
    }
}
{
    "_id" : ObjectId("5e300c9673f256100d5ca0af"),
    "geometry" : {
        "type" : "Point",
        "coordinates" : [
            -102.5,
            22.6
        ]
    },
    "properties" : {
        "@timestamp" : ISODate("2019-01-01T12:01:00.158Z")
    }
}
{
    "_id" : ObjectId("5e300c9673f256100d5ca0b0"),
    "geometry" : {
        "type" : "Point",
        "coordinates" : [
            -104.5,
            21
        ]
    },
    "properties" : {
        "@timestamp" : ISODate("2019-01-01T12:10:00.158Z")
    }
}
{
    "_id" : ObjectId("5e300c9673f256100d5ca0b1"),
    "geometry" : {
        "type" : "Point",
        "coordinates" : [
            -104.5,
            21
        ]
    },
    "properties" : {
        "@timestamp" : ISODate("2019-01-01T13:10:00.158Z")
    }
}

Index:

{
    "v" : 2,
    "key" : {
        "_id" : 1
    },
    "name" : "_id_",
    "ns" : "test_database.map_reduce_test_data"
},
{
    "v" : 2,
    "key" : {
        "properties.@timestamp" : -1,
        "geometry" : "2dsphere"
    },
    "name" : "properties.@timestamp_-1_geometry_2dsphere",
    "ns" : "test_database.map_reduce_test_data",
    "2dsphereIndexVersion" : 3
}

Query:

db.map_reduce_test_data.find({"properties.@timestamp": { $gt: new Date("2019-01-01T12:00:00Z"), $lt: new Date("2019-01-01T13:00:00Z") }})

Explain result:

{
    "queryPlanner" : {
        "plannerVersion" : 1,
        "namespace" : "test_database.map_reduce_test_data",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "$and" : [
                {
                    "properties.@timestamp" : {
                        "$lt" : ISODate("2019-01-01T13:00:00Z")
                    }
                },
                {
                    "properties.@timestamp" : {
                        "$gt" : ISODate("2019-01-01T12:00:00Z")
                    }
                }
            ]
        },
        "winningPlan" : {
            "stage" : "COLLSCAN",
            "filter" : {
                "$and" : [
                    {
                        "properties.@timestamp" : {
                            "$lt" : ISODate("2019-01-01T13:00:00Z")
                        }
                    },
                    {
                        "properties.@timestamp" : {
                            "$gt" : ISODate("2019-01-01T12:00:00Z")
                        }
                    }
                ]
            },
            "direction" : "forward"
        },
        "rejectedPlans" : [ ]
    },
    "ok" : 1
}