Currently, blackout windows can only be global. They should be allowed to be created for a CI or set of CIs like Maintenance windows can be. Some CIs should not allow changes to occur during because critical customer processes occur during that time for that individual CI. You can also have a situation where Security Patches are scheduled on certain CIs for a specific date/time. Changes should not be allowed during those windows because the server will be rebooted, causing an issue with whatever change was being applied when the CI was rebooted.