Well I'm planing too make quite a few alchemy items but I don't see how long they take too craft just the craft dc.
Look up crafting in the core rule book it will explain it. Also I recommend the master alchemist feat from I believe the APG.
A short break down is you roll a check of craft alchemy if you succeed multiply the dc by your result and that's how many silver peices of the items total cost you have finished that week.
K thanks for the help I'm still trying too figure out how much time is needed too make all the items i want but i will get it soon.
All depends in what you roll.
It's impossible to give an exact amount of time it will take, because how much of the item gets made each week depends on your craft roll. Somebody who keeps checking 20s on his Craft (Alchemy) will make his item far faster than somebody who keeps checking 25s. A breakdown of why:
Let's say you're making a Tanglefoot Bag. Checking the rules on crafting, we find that we're going to need to spend a little over 166 silver pieces to make it, and we're going to need a total of our check times the DC greater than 500 in order to finish the item (check x DC >= 500 to finish item, may add multiplied results together until is greater, so two weeks with a result of 20 both weeks would result in 800 silver worth of progress).
So, that guy who's getting 20s on his Craft makes 400 silver in progress per week (because 20 result x 20 DC = 400 progress), so he finishes it in about 2 weeks (or at least 1 week and a few days).
The guy who's getting 25s makes 500 silver in progress per week (because 25 result x 20 DC = 500 progress), so he finishes his bag in only a week.
Hope that helped clear things up a little bit.
A good way to estimate is to figure out what you'll get by taking 10 on your roll and, assuming taking 10 will pass the check, plugging that into the equation I outlined above.