To enter a location with a hidden object scene, tap/click on its building on the map.
In the scene, you need to find the items from the search list before the time runs out.
When you re-enter the location, the search items may look different and may be found in different places.
Tapping/clicking on objects that are not on the search list two to three times within a second will reduce the time limit by 5 seconds. The time penalty increases with each subsequent mistake.