Answer
The retention window itself (currently 30 minutes) is a fixed constant and can't be changed in the current version. What you can adjust is the schedule of the Light Cleanup batch job that enforces it — it runs every 10 minutes by default and deletes anything older than that 30-minute threshold, so widening its execution interval effectively extends how long FndTempLobs data survives before cleanup, without changing the 30-minute constant itself.