Значение временного интервала будет таким, как показано ниже
"intervals": "2018-05-07T00:00:00.000/2018-05-21T00:00:00.000"
Нет квадратных скобок. Ниже приведен пример запроса topN -
{"aggregations":[{"name":"count","type":"count"},{"fieldName":"fname1","name":"fname1","type":"longSum"},{"fieldName":"fname2","name":"fname2","type":"longSum"}],"dataSource":"xxx","dimension":"dim1","granularity":"all","intervals":"2018-05-16T00:00:00.000/2018-05-17T00:00:00.000","metric":"count","queryType":"topN","threshold":4}