Help with golang app

I have this code:
package main

import (

"encoding/json"

"fmt"

)

// JSONMap is a specialization from map

type JSONMap = map[string]interface{}

// JSONAggregation is a specialization from map[]

type JSONAggregation = map[string][]interface{}

// JSONtoMap convert the json string to a JSONMap compatible with Go

func JSONtoMap(originalJSON string) JSONMap {

var result map[string]interface{}

json.Unmarshal([]byte(originalJSON), &result)

return result

}

func aggregateInterfaces(aggregation *JSONAggregation, target JSONMap) {

ref := *aggregation

// iterate through every target (JSONMap) and append it to the aggregation

// if its the first time the key is seen, then allocate memory

// and then append it

/*layout := "2006-01-02T15:04:05.000Z"

t, err := time.Parse(layout, fmt.Sprint(target["date"]))

if err != nil {

    fmt.Println(err)

}*/

if v, found := target["date"]; found {

    fmt.Println(v)

    str := fmt.Sprint(v)

    fmt.Println(str[11:13])

}

for key := range target {

    if _, ok := ref[key]; ok {

        ref[key] = append(ref[key], target[key])

    } else {

        ref[key] = make([]interface{}, 0)

        ref[key] = append(ref[key], target[key])

    }

}

}

// aggregateJSONS return a JSONAggregation with all jsons aggregated

// given that is provided an array of jsons on string format

func aggregateJSONS(jsons []string) JSONAggregation {

aggregation := make(JSONAggregation, 0)

for _, result := range jsons {

    aggregateInterfaces(&aggregation, JSONtoMap(result))

}

return aggregation

}

func main() {

jsons := []string{

    `{

        "name":"kate",

        "date":"2012-04-23T18:24:59.511Z",

        "data":"is nice"

    }`,

    `{

        "name":"gleison",

        "date":"2012-04-23T18:25:00.511Z",

        "data":"is a good person"

    }`,

    `{

        "name":"breno",

        "date":"2012-04-23T19:25:01.511Z",

        "data":"is a cool person"

    }`,

}

fmt.Println(aggregateJSONS(jsons))

}

And it the end i got
2012-04-23T18:24:59.511Z

18

2012-04-23T18:25:00.511Z

18

2012-04-23T19:25:01.511Z

19

map[data:[is nice is a good person is a cool person] date:[2012-04-23T18:24:59.511Z 2012-04-23T18:25:00.511Z 2012-04-23T19:25:01.511Z] name:[kate gleison breno]]

My question is: how can i take an access to the field “date”. What i need to do: aggregate them to groups by hours, days, weeks and months. Categorize them and then aggregate. How can i compare date’s by each other?