The application licensing docs say that once the application is no longer refundable, the validity period of license server responses is "typically a number of days." This is rather vague, although I would imagine that it means "days, not weeks or months" (as opposed to "days, not minutes or hours").
Does anyone have actual data about the VT field values when the Android Market license server returns a LICENSED response?
In my experience the period is 14 days for a live application and 1 minute for a test response. It's possible to ignore the VT value and use your own timestamp (or add extra time to it) by altering the long value stored.
I've never seen these values documented and recall them from development around 3 months ago.