Run test at a fixed time

What does this MR do?

Temporarily fix broken master #295173 (closed)

Due to how HLLRedisCounter#weekly_redis_keys converts dates to calendar week, it would result in an empty array when the calendar week of end_date occurs before the calendar week of start_date.

For example, given start_date 2020-12-01 and end_date 2021-02-01, the calendar week would be reversed, resulting in empty array from #weekly_redis_keys