Extended Persistent Spells? [3.5]

[Fortuna]

Does it work? Can I get 48-hour duration spells?

[Yuki Akuma]

It should work - you can apply metamagic feats in whatever order you like, and as 24 hours is a duration, Extend Spell can double it.

[arguskos]

Yeah, this one technically functions, since there is no called out prohibition on them stacking favorably, such as that Maximize and Empower have.

[nargbop]

Agreed. Page 88 of the PHB makes no mention of the order that metamagic feats must be applied. Extend Spell PHB 94 doesn't either, and neither does Persist Spell CArc 81. You should be able to Extend a Persisted Spell for 48-hour-duration.
As always, check with your DM before trying to pull it off in game.
Note that when you are spending your high-level slots for Persisted effects, one enemy's Dispel check will make you sad.