A system.buckets collection should be indexed on `control.max.time`.

We may create one or two secondary indexes depending on whether a metadata field is configured for the time-series collection:

• Defining a meta field results in two more secondary indexes:
  • { meta: 1, control.max.time: 1 }
  • { control.max.time: 1, meta: 1 }.
• If no meta field is defined at time series creation time, just one secondary index is created, on { control.max.time: 1 }.