Well, that solution only works if the ceiling is low enough to reach the light bulb. What if the ceiling is 20 feet?
I think I got a better solution.
Considering that this is a hypothetical scenario and considering that you are allowed to use as much time as you like there is another way to figure out this question.
1.You flip the first switch, and leave it turned on for four years (way beyond the normal lifespan for such a bulb)
2. After 4 years you return and flip the second switch.
3. You then open up the door and walk inside;
a) If the room is dark, you shine a flashlight at the bulb to establish whether it has burn marks or not. If it has such burn marks, then you know for a fact that the first switch operates the light.
b) If the bulb doesnít exhibit such burn marks then you know that itís the third switch that operates the light.
c) If the light is turned on, then you know that itís the second switch that operates the light.
This scenario will only work if it was a brand new light bulb, or sufficiently unused for such burn marks to have materialised.