I ran a test in a controlled environment to see how well the PLA will react to the heat of the tea light.
I let the candle burn to extension. The plastic softened and it deformed a little, making a small bump underneath. To be honest, I was expecting worst than this.
I do not advice anyone to put a real tea light candle in this box, especially if it's printed from PLA. If you do, don't leave it unattended.