A Day selected in the date-picker means
00:00:00 when a single day or the beginning of a period
23:59:59 when the end of a period
Today: 00:00 of the present date until the present moment.
Yesterday: 00:00:00 to 23:59:59 of the preceding day.
This Week: First day of week until the preceding day.
Last Week: The last complete calendar week (Sunday/Monday to Saturday/Sunday).
Last 7 days: The last 7 days, excluding today.
Last 30 days: The last 30 days, excluding today.
Month to date: The 1st of month until the preceding day.
Last month: The last calendar month.
Year to date: Jan 1st of this year until the preceding day.
Last year: The last calendar year.