queries on Date type results empty search results

there are two issues here
1) by default when we try to store date in jcr it saves in below format 2017-08-21 21:35:33 when i perform query on this date it is showing empty search results.
select [body/dataNum] from [cas:article] where [jcr:lastModified] = '2017-08-29 16:36:39' order by [jcr:created] DESC
2) when i try to use
select [body/dataNum] from [cas:article] where [jcr:lastModified] cast('2017-08-29 16:36:39' as date) order by [jcr:created] DESC it is throwing an error not a date string, after some investigation i found that it will accept only ISO8601 format (yyyy-MM-dd'T'HH:mm:ss.SSSZ). when i try to store date in above format it automatically converts to yyyy.MM.dd HH:mm:ss .
now my questions are
1) how to change default date format of jcr to yyyy-MM-dd'T'HH:mm:ss.SSSZ
2) how to perform queries on Dates