My current gig is using Scylla for storing time series data, we're partitioning by day and anywhere from 5-15 million rows per day.

We've mostly been using Apache Beam/Cloud Dataflow for working wtih the data en mass for occasional reports, and we're planning on trying Presto soon as well. I'm interested in what solution you come up with, happy to chat more about this kind of thing on twitter or email.