Wood generally doesn't rot unless it gets wet. Wood is typically treated so that if it gets wet there is a mechanism to prevent fungi from eating it. Painting it, for example, causes the water to slide off the wood before the underlying wood can get wet. But even a tiny puncture of that paint will expose the wood to rot causing fungi that float in the air everywhere. Most wood already has rot causing fungi inside of it, all you need to do to activate it is add water.
Woodbugs are another water loving creature. No water, no problem.
I've got a balcony who's floor is made out of wooden planks. It was varnished at some point, but the varnish is damaged in many places, how long before the wood degrades completely and is unsafe to stand on?
Usually the planks under a balcony are protected by the balcony itself, so they remain fairly dry, especially if there are drip flashings that redirect rain drips and rivulets away. Or, they may be pressure treated wood, in which case it's likely to outlast the building whether it gets wet or not. There might be a fascia board that is designed to take the rain and rot away, separated from the structural beams by a flashing, vapor barrier, standoffs, hidden paint/stain, or nothing!
Woodbugs are another water loving creature. No water, no problem.
Dry old furniture can last a millenia.