What happens when a Generator Invoker casts a spell with the Lingering Spell Meta-magic feat.
Lingering Evocations (Su): Any evocation spell you cast with a duration greater than instantaneous lasts an additional number of rounds equal to 1/2 your wizard level (minimum +1). At 20th level, any dispel checks made against your evocation spells must be rolled twice, and your opponent must use the less favorable result.
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Lingering Spell (Metamagic)
You spell clings to existence, slowly fading from the world.
Benefit: You may cause an instantaneous spell that affects an area to persist until the beginning of your next turn. Those already in the area suffer no additional harm, but other creatures or objects entering the area are subject to its effects. A lingering spell with a visual manifestation obscures vision, providing concealment (20% miss chance) beyond 5 feet and total concealment (50% miss chance) beyond 20 feet.
A lingering spell uses up a spell slot one level higher than the spell's actual level.
Specific example
8th level Generator casts Lingering Fireball
Strictly speaking, Lingering Spell doesn't say it increases the duration — only that the effect persists until the beginning of your next turn. Some rules lawyers would say the spell still has a duration of instantaneous and wouldn't be altered by Lingering Evocations.
Personally, I'm kind of torn on the issue, and think there's room for debate. I'd probably play it safe and would refrain from using the combo against another GM or my players, unless they insisted on using it first.