The options to filter by date/time are as follows:

The "Today's Activities" button filters the results to show activity for the current day. Click the "Today's Activities" button to use the filter. This filter is applied as default when you first access the activity monitor.
"Date (from)" provides filtering of activity from that date/time. It is possible to see activity up to one month in the past.
"Date (to)" provides filtering of activity up to that date/time

Searching by date/time: Using the "Date (from)" and "Date (to)" filters
Date: click the button and then select the date from the date grid.

Time: click the button and then select the time from a time list.

Click "Apply" to run any selected filters.

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