Customize Built-in Reports

I frequently use the Spending over Time report.  The report defaults to the "Last 12 Months" report which is exactly the report that I want to customize to show monthly spending over 12 months..  As I write this (April 7,2019), the default report shows all transactions from April 1, 2018 through the present day.  I want to to customize to create a true 365 day report from April 8, 2017 through the present day (April 7, 2019).  In other words, I want the report to show true 365 day monthly spending.  As far as I can tell, the customize menu only allows the user to pick the month and does not permit a specific day to be chosen. When I choose April 8, 2018 as the start day, the report still shows all data from April 1, 2018. Thanks for any help or advice,