insights: Make insight start times consistent between just in time and backfilled insights.

Created by: chwarwick

When resolving just in time capture group insights, the current time is used as the start of the time frame. The start of the day should be used so that the chart values remain consistent across refreshes within the same day.

Updated 4/23: Currently the time for the most recent data point after creating an insight is inconsistent depending on if it is calculated just in time or if it is populated by the backfill process.

Additionally because just in time capture groups use the current time as the starting point the historic datapoints can shift over the course of the hour or day.