Reverse-engineer alchemical item formulae- time?

[dien]

It says in the Core, under the Formula rules, that reverse-engineering "...uses the Craft activity and takes the same amount of time as creating the item from a formula would."

But how long precisely is that? As an alchemist, I craft over a dozen items from formula when I rest/study/etc. In the craft rules, it says that crafting an item takes 4 hours. Which is the correct time frame to use for reverse-engineering items?

[Super Zero]

It takes four days to craft an item at full cost, or longer at a reduced cost. Alchemist class features give you free temporary items, but that's not crafting them (which all alchemists can also do, since they get the necessary feat, skill training, and formulas automatically).

[dien]

Alright, thank you.