This is a cool little patch! It's a simple addition, but it really opens the door to a lot of clever setups.
To clarify just a little bit from the description, the time limit is only applied to clouds that are inserted with extra bit = 1; clouds with extra bit = 0 will still last forever. Note that when a time-limited cloud disappears, it's gone for good, so plan your levels accordingly.
Tested with Asar 1.71, Lunar Magic 3.04, SA-1 1.32, PIXI 1.2.9, Snes9x 1.59.2.