We've gotten some clarification from Google regarding any changes to the app refund window in the Android Market after a couple of developers led us to believe it had been changed to 48 hours when asked to accept a new version of the Developer Distribution Agreement. The short version is there have been no changes. You still have 15 minutes to uninstall an application for an automatic refund.
The 48-hour window is for Google to refund the money to the developer. Also, you, as a user, technically have 48 hours to request a refund of an app from Google, though very few people do that for the obvious reason.
Hope that clears things up a bit.