OCC 12
I don't have the DFRPG books, but I believe it's the same as GURPS:DF. DF1 page 20 (right column, about halfway down the page) has Create spells only lasting a day, but doesn't give any information about spending extra energy to make them last longer. The latter may have been a house rule or something added in DFRPG (or might be in Power Ups, which I don't have), but I'm sure I recall it from when Chou-Zhen was going to make gravestones by Shaping Earth then transforming Earth to Stone (after the battle with Pequenaud's troops) -- but wound up spending the energy to Shape Earth on natural stones at the higher energy cost because that effect would be permanent.