Burning a candle for too long can cause carbon build-up. This will cause the flame to be too high and create a bigger risk of fire. For this reason, it is recommended to limit candle burning to 4 hours. See the link below for more information.
https://upcandledesign.com/blogs/mindful-artistry/candle-mushrooming-what-it-is-and-how-to-prevent-it
