Using System.Date in a Smart List Filter

I want to build a smart campaign with a smart list looking for the Updated At field is always today.  When I click today on the calendar it selects today's date (5/1/2018) and tomorrow the 5/1/2018 is still in the filter.  I want this date to be dynamic and always be the current day.  I know system.date is a dynamic date field but the system won't let me put this in the field for the date in the filter.  How can I filter my smart campaign list to accomplish the Updated At is always the current date? I need step by step instructions.