Are players able to swap out magic items continually and get the immediate effect of their enchantment?
Example: A character has a Ring of Transportation, Ring of Protection, and a Ring of Invisibility. Can they swap them around all within the same day/encounter to get the benefit?
I was under the assumption that magic items needed to be worn for 24 hours before they work, but this could be an old rule that never translated to Pathfinder.
While some Pathfinder magic items do need to be carried or worn for some period of time before their full benefits are realized, unless the magic item specifically says in its description that it must be, it does not need to be, and all of its benefits can be realized immediately by the next lucky fellow to pick it up or don it, and it can be passed around from person to person at will.
For example, the headband of vast intelligence has a noticeable but still lesser effect until its been worn by the same creature for 24 hours and the ring of sustenance must be worn continuously by the same creature for a week before its effects kick in at all, but the rings of invisibility, protection, and transposition can benefit their wearers right away… although such a wearer must still discover the command word necessary to activate the ring of invisibility or ring of transposition.
The idea that magic items need time to attune to a new possessor is, to my understanding, a more modern rule, largely atypical of magic items in Pathfinder and its antecedents, although several late-era dnd-3.5e magic items also require such a warm-up period.
I can provide only a proof by contradiction that magic items function before they've been equipped for 24 hours.
Assumed for Contradiction: An item does not function without first being equipped for 24 hours.
Given: Belt of Giant Strength
Belt of giant strength implies that it has effects before 24 hours have passed, but does not explicitly state it grants the referenced temporary ability bonus.
Therefore, we can conclude one of two possibilities:
1) The item at no time grants the temporary ability score bonus provided for in the item description, per the assumption for contradiction.
or
2) The item grants the temporary ability score bonus that it provides for during the first 24 hours of its being worn.
Now this is where you get into some RaI territory, wherein we must suppose a designer would not introduce a rule which was never actualized in practice. This would lead us to reject the first outcome. If you do so, we arrive at a contradiction, which yields the conclusion that the negation of our assumption is true, which is: An item does function without first being equipped for 24 hours.
Furthermore, if there is not a rule in the text stating that items must or must not be worn for some amount of time before taking effect, proving either assertion false directly will be difficult due to the lack of falsifiability inherent in such a system.
