Nifft said:No, because metamagic feats don't interact with each other (see Maximize + Empower for an example).
You get a Maximized fireball on the first round, and then next round you'd get a regular fireball.
Maximize + Empower is a specific example detailing interaction where none should exist. (a Maximized spell doesn't have a variable effect any more...)
However, it's silly to apply that ruling to other metamagic feats.
Would you rule that a Cold-substituted Widened Fireball does cold damage within 20' of the center, then 20' of fire damage around that?
Would you rule that an Extended Widened spell would suddenly shrink when half it's duration expires?
What's the casting time of a Quickened Twinned Fireball? Surely it's still one swift action.
Metamagic is expensive enough as-is; it's illogical for it not to be multiplicative.