Is Parallel Query Execution supported in Druid ..?

Hi,
i Just want to calculate cohort analysis( retention analysis) for 7 days, by following the documentation http://druid.io/docs/latest/development/extensions-core/datasketches-aggregators.html#retention-analysis-example , i can get the retented users, but the problems is i need to construct a cohort chart for 7 days so i decided to calculate each and every day, Example : if i need to calculate cohort chart from 21st to 27th , starting from 21st ( day 0, day 1, … day 7), and 22nd (day 0 … day 7). so i constructed theta sketch aggregation For each Day and run all Queries simultaneously. but it takes around 20 seconds of time to execute last aggregation i:e(27th Day 7) . but when i execute independently ( 27th day 7) iam getting result in 500 ms. is my approach is correct. to get the cohort chart ?