Hi Youngsol, you can't specify multiple granularities in a single spec ... you can only have compaction/reindex jobs change the granularity for specific time intervals they operate on.
There is the notion of multi-stage auto-compaction that may be added to the product in the future as part of data lifecycle feature development ... but for now the common practice is to ingest at one granularity, and then manually run compaction/reindex jobs at the appropriate time to convert aging time intervals to the new desired granularity. I know people are doing what you are describing ... all using these batch jobs.