Each histogram bar should represent the values between the start and end of a time period. If we have some datapoint `{x: 9:30, y: 12}` and a bucket size of `00:05`, it would be more accurate for its bar to represent the time period from `9:25` to `9:30` than for it to represent the time period from `9:30` to `9:35`, since none of the values that aggregated to `12` occurred after `9:30`.

This wasn't a problem before, since the first bar was 'hidden' in the svg, but now that we have a margin, it is partially visible.

Up for alternatives.