mysql converting from UTC to IST
IST is 5.30 hours ahead of UTC, so when 13th starts in IST i.e. 2015-03-13 : 00:00:00
its 2015-03-12 18:30:00
in UTC
mysql> select convert_tz('2015-03-13T00:00:00+00:00','+00:00','+05:30') ;
+-----------------------------------------------------------+
| convert_tz('2015-03-13T00:00:00+00:00','+00:00','+05:30') |
+-----------------------------------------------------------+
| 2015-03-12 18:30:00 |
+-----------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
And when 13 ends in IST i.e. 2015-03-13 : 23:59:59
its 2015-03-13 18:29:59
in UTC
mysql> select convert_tz('2015-03-13T23:59:59+00:00','+00:00','+05:30') ;
+-----------------------------------------------------------+
| convert_tz('2015-03-13T23:59:59+00:00','+00:00','+05:30') |
+-----------------------------------------------------------+
| 2015-03-13 18:29:59 |
+-----------------------------------------------------------+
So yo get the data in IST for 13th you will need to search data within this range of dates.
So the condition would be as below -
s.created_at
between convert_tz('2015-03-13T00:00:00+00:00','+00:00','+05:30')
and convert_tz('2015-03-13T23:59:59+00:00','+00:00','+05:30');
and since you are doing conversion at the time of select so it will return all 13th data.