Wet bulb temperature is basically converting to 100% humidity equivalent, so as you get closer to 100%, WBT approaches measured temperature. We use this metric because our bodies cool mostly via evaporation, and no evaporation is possible at 100% — the air is already fully saturated. So in general, WBT means minimum possible temperature that can be reached by evaporative cooling. Once your body loses the ability to cool, it rushes to match surrounding wet bulb temperature (or even exceed it, since we produce about 100W of heat energy by simply existing).
So 52C at 90% is about 50C WBT. Survivable for mere minutes for some, and probably for about an hour or so for most humans. Definitely not survivable for a full day.