test.go

package main

import (
	"encoding/json"
	"github.com/tidwall/buntdb"
	"github.com/tidwall/gjson"
	"log"
	"strconv"
	"time"
)

type Order struct {
	Oid      int
	Statuses []Orderstatus
}
type Orderstatus struct {
	Sid  int
	Time string // 2017-05-01T00:00:00Z
}

//compareDates is a special function which extracts dates from status=6 and compare then
func compareDates(a, b string) bool {
	astr := gjson.Get(a, `Statuses.#[Sid=6].Time`).String()
	bstr := gjson.Get(b, `Statuses.#[Sid=6].Time`).String()
	start, err := time.Parse("2006-01-02T15:04:05Z", astr)
	if err != nil {
		return true
	}
	end, err := time.Parse("2006-01-02T15:04:05Z", bstr)
	if err != nil {
		return false
	}
	// log.Printf("Compared %s %s \n", a, b)
	return end.After(start)

}

func main() {
	// Some data
	os := []Order{
		Order{Oid: 1, Statuses: []Orderstatus{Orderstatus{Sid: 1}, Orderstatus{Sid: 2, Time: "2016-03-17T12:57:51Z"}}},
		Order{Oid: 2, Statuses: []Orderstatus{Orderstatus{Sid: 2}, Orderstatus{Sid: 6, Time: "2016-03-17T10:58:03Z"}}},
		Order{Oid: 3, Statuses: []Orderstatus{Orderstatus{Sid: 3}, Orderstatus{Sid: 6, Time: "2016-03-17T15:58:03Z"}}},
		Order{Oid: 4, Statuses: []Orderstatus{Orderstatus{Sid: 5}, Orderstatus{Sid: 6, Time: "2016-03-17T20:58:03Z"}}},
	}

	db, _ := buntdb.Open(":memory:")
	//Store them
	db.Update(func(tx *buntdb.Tx) error {
		for _, o := range os {
			buf, _ := json.Marshal(o)
			tx.Set(strconv.Itoa(o.Oid), string(buf), nil)
		}
		return nil
	})
	//Build index with our function
	db.Update(func(tx *buntdb.Tx) error {
		err := tx.CreateIndex("sid", "*", compareDates)
		return err
	})
	db.View(func(tx *buntdb.Tx) error {
		pivots := []string{
			`{"Statuses.#[Sid=6].Time:"2016-03-17T12:58:03Z"}`,
			`{"2016-03-17T12:58:03Z"}`,
			`{"Time":"2016-03-17T12:58:03Z"}`,
			`2016-03-17T12:58:03`,
		}
		for _, pivot := range pivots {
			log.Printf("pivot=%s:\n", pivot)
			tx.AscendGreaterOrEqual("sid", pivot, func(key, value string) bool {
				var order Order
				json.Unmarshal([]byte(value), &order)
				time := gjson.Get(value, `Statuses.#[Sid=6].Time`)

				log.Printf("key=%s, sid=%s\n", key, time)
				return true
			})
		}
		return nil
	})
}

Try this pivot {"Statuses":[{"Sid":6,"Time":"2016-03-17T12:58:03Z"}]}