code: func NewObjectIdWithTime(t time.Time) ObjectId {
  	var b [12]byte
  	binary.BigEndian.PutUint32(b[:4], uint32(t.Unix()))
  	return ObjectId(string(b[:]))
  }
docs: // NewObjectIdWithTime returns a dummy ObjectId with the timestamp part filled
  // with the provided number of seconds from epoch UTC, and all other parts
  // filled with zeroes. It's not safe to insert a document with an id generated
  // by this method, it is useful only for queries to find documents with ids
  // generated before or after the specified timestamp.