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In the Timeline view, I'd love to see a slightly more granular hourly view than "Day split into hours." Most of the records in my base are no more than an hour long, and there tend to be a few phases of the day where they bunch up a lot, which makes the "Day split into hours" zoom level really difficult to read. If there were something more zoomed in, even something as simple as "12 hours split into hours," that would help a lot. (The ability to freely zoom would be even better, but that might be too much to hope for!)
When it comes to looking at shorter-duration events at a glance, the calendar view is easier to read, but Grouping is where the Timeline shines, and exactly what I need it for.