It would be a good idea to be able to attach Label to dates. It will help correlate the events with a trend change. For example "New Release deployed" or "New marketing campaign rolled out" will help understand the significant trends change.
Some of the desired features i could think of
Add friendly label(s) to a date.
Labels should be visible for each report under the report suite or org.
An additional capability to toggle the label visibility at report level or in the reporting UI/workspace will be great. For instance if there are 2 labels associated to a date, i should be able to keep one and hide the other.