The time interval depends on how often your poller runs, and when it was created. For example, if you create a default five minute poller at 12:30, then it will run at 12:35, 12:40, 12:45, etc.
Yes, all reports are based on the data retrieved by the poller. The device report is an amalgamation of all poller data for the various built-in templates.
Data can be retained on a configurable basis. The data purge settings can be found under HUM > Admin > Data Purge. By default, the 12 hour summarization data is kept for a year. But there are a lot of data purge metrics that can be configured.
As long as the data exists in HUM, you can access it via the HistoGraphIt portlet, or via reports.
