When you are running a Hotsheet from the widget on the Matrix home page, you have several different options for the time frame/days back within which you are looking for changes:
Since Last= see changes since the last time you ran the Hotsheet search.
This Session= see what has changed since you have been logged into Matrix.
24 Hour= see changes in the last 24 hours.
Today= see changes for the calendar day.
3 Day= see changes over the last 3 days.
7 Day= see changes over the past 7 days.
Custom= set up your own custom time frame.