Jim,
I do not think there is a property can you set to be a different default than 7 days. I know you can change the filter and then save it, but it is just during the session the browser is up. You can change it to Last Hour, Save filter options (Last Hour), log out of the user and then log back in and it will be there. But if the Portal UI is closed, once you log back in, the Summary goes back to the default of 7 days.
~Marcy