## By the rules it can be used multiple times per day, but it does what your DM says it does

The condition for activation is: 

> Whenever the wearer of this ring takes the withdraw action or becomes helpless (including falling unconscious)

The withdraw action only makes sense in combat, as it states:

> Withdrawing from melee combat is a full-round action. 

There are, rules as written, no additional limitiations that say it that it only can be used in combat or that it would be limited to a given number of times per day. You can compare this for example to a [Ring of Grit Mastery][2], which says

> **Once per day**, as a standard action, the wearer of the ring can (...)

If there was a limitation on uses per day, you would expect similar language in the ring's description.

It would not be overpowered to allow using it multiple times per day, because that is how the item has been published in the printed rules (if you allow the idea that the rules as given are balanced; they may not fully be).

Allowing to use it outside of combat also should not cause balance issues, as [Hey I Can Chan points out][1]: you can obtain a *wand of invisibility* in the same price range, that can be used any time, and is more generally useful as a way to become invisible.  

That said, if your DM rules the ring only works once per day, then that is what it does. The rules say this about the matter:

> Just as GMs arbitrate the rules within their games, so can they manipulate, repurpose, and wholly invent new rules to improve their games. 


  [1]: https://rpg.stackexchange.com/questions/201666/can-the-decoy-ring-be-used-multiple-times-per-day/201667?noredirect=1#comment550810_201667
  [2]: https://www.d20pfsrd.com/magic-items/rings/ring-of-grit-mastery