I am not aware of a timer feature for the refresh your can set alerts these are well described in the Help Section for CR.
As far as refresh, I suppose you could set the report to run as a scheduled task at regular intervals, when the report loaded you see the alert.
You could also build an application that would run in the background or service with a timer that would effectilvely refresh the report and any resulting alerts message showing.
Perhaps someone else can make note of other choices.
Let us know what you decide to be a solution.
Regards,
John W