Both the Savings and Savings Trend dashboard widgets allow you to view historical, finalized savings information. During a given month, you'll be able to view savings information for previous months (e.g. on April 18th, you'll be able to see March and back).
In the first few days of a new month (roughly the 3rd to the 5th), AWS finalizes cost and usage information for the previous month. As soon as ProsperOps detects this finalization, we refresh the Savings and Savings Trends widgets and send all users on the account a monthly summary email. That email is a good trigger to check the ProsperOps Console for updated savings information.
Please note that while the Savings and Savings Trend widgets currently show only finalized savings information, ProsperOps is real-time monitoring your EC2 environment for change and continually managing an optimal RI portfolio that maximizes your savings. Those savings are being generated every second of every day, but are only reflected in the ProsperOps Console dashboard once they have been finalized by AWS.