That’s probably easier using a Timer node.
When your character leaves the shop start a Timer to call ResetInventory (or whatever) after 10 minutes (600 seconds) have passed. If the character returns while the timer is still running, stop the timer.
I haven’t actually used timers yet in Unreal 4.9, but the system looks fairly straightforward. In a quick test, I didn’t get any errors or warning trying to clear an uninitialized handle (when first entering the shop, the variable hasn’t been set yet).
If you need to save the timer to continue at the same time when loading a savegame, you can use Get Timer Remaining Time and save the returned float value. Then when loading your savegame and this value is greater than zero, simply restart the timer (using Set Timer By Event) with the remaining time instead of the full 10 minutes.
Good luck!