Scroll of Spell Extension

Does anyone know how precisely the Scroll of Spell Extension works? I have noticed a few times that my hastes or stealths or undead protections last a lot longer than they should. However, when I've *tried* to use a scroll of spell extension it doesn't seem to make any difference. Do you cast the spell, then read the scroll? Do you read the scroll and it affects the next spell? Is the extension so minor that I just didn't notice? Or does it only work with spells that you cast and not scrolls or potions?

Also, if you read a scroll of Time Warp and go back 5 mobuls, does it extend your spells? When you cast Haste, does it expire at a certain fixed "time" or does it run for one mobul regardless of Time Warp?

I wish I had the time/know-how to look through the larn source code, but I don't. Time Warp and Spell Extension are just two of the things that have always befuddled me about Larn. (The previously mentioned Amulet of Invisibility falls into that same catagory).