This is probably going to be a noob question but I can't find the answer in the core rule book.
With the wondrous item Hat of Disguise. It says you can cast the alter self spell and lasts for 10min/lvl and when you interact with somebody they make a will save to see if it is an illusion.
What I want to figure out is what determines the time limit and the will save check. Does it get determined on discovery/creation or does it increase by whomever uses it.
For example a 10th lvl rogue uses it and the will save is 10+1+10=21 will save. Or it was a created by a 6th lvl user and thus has a 10+1+6=107 will save while still being used by a 10th lvl rogue.