In the Date of Activity filter, from my testing it seems like "between" includes dates entered in the two date fields. The definition in the help article here for between = only events between the selected dates, doesn't clarify that. It would be nice if that was updated.
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Yes, the 'between' filter is inclusive, so a selection of dates "between March 15 and March 17" for instance would be the three days: March 15, 16, and 17.
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