I've actually been able to create fully statted NPCs in less than 5 minutes with True20; something I could never do with d20 systems.
Abilities are easy; just needs to add up to four or six. This is faster than rolling dice, especially when doing multiple NPCs at once.
With only three classes and no prestige classes to consider, picking a class takes almost no time.
Without skill points or cross-class skills, you're just picking a few skills. Much, much faster for high-level NPCs.
Picking feats is the hardest part, but without bonus feats or class abilities to worry about, and with far fewer prequisites, it's very easy to know how many feats (level+3) and can even be done with minimal references to the book once you have some practice.
Without gold pieces and the magic item economy equipping characters is pretty fast and easy. We no longer have shopping nights in my games.
Finally, the hard part of putting together spell books, known spells and prepared spells is completely eliminated. In fact, thanks to the fact that it's driven by feat selection, it's no harder to put together a high-level spellcaster than a high-level warrior.