granularity (1m by default). Shows order placement and cancellation rates over time. Buckets: each bucket is labelled by its open time in UTC, and buckets open on multiples of the bucket width since the Unix epoch. A bucket with no order events is omitted. A bucket counts only the events inside [start, end), so when start or end falls inside a bucket, that first or last bucket is partial; start and end on bucket opens give whole buckets.