Do alchemists with Swift Alchemy take half as much time to brew potions? What exactly is an "alchemical item"? Anything that can be made with Craft (Alchemy) ?
They can be created using Craft (Alchemy) rather than Spellcraft, and this is still limited by the 1 magic item / day crafting limit.
Even the most powerful potions an alchemist can brew are only base price 750g, meaning it will take a maximum of 1 day of crafting. During this day, the alchemist must spend 8 hours uninterrupted, or 4 hours with a +5 DC to craft.
So as far as I can see, the only benefit will be a decrease from 8/4 hours to 4/2 hours, and then further decreased to a full round action at level 18 with Instant Alchemy, which still seems perfectly reasonable given the 1/day limit and the spell level cap of 3 on potions.
Are there any loopholes I'm missing that would make such an inference a bad call? It seems safe to allow this, but I feel that the rules would have been more explicit about allowing it if potions are indeed meant to fall under this ability.