On Apigee Edge On premise, at present when you select the duration for custom reports it allows you to select a by default a maximum of 15 days in calendar. If you need to change this settings to have a bigger value, you have to make changes in the Apigee Management Server component level.
There is a property called ‘apigee.feature.enableForceRangeLimit’ you can set in apigee.conf on the management server.
Please refer to the below doc for more details:
http://docs.apigee.com/analytics-services/content/using-analytics-dashboards