High glaze firing takes the kiln up to just over 2300° for cone 6 stoneware. That usually takes about 14 hours or so and then the cool down takes another who knows what. I just know I have to tie my hands down to my sides and not go anywhere near the kiln for 30 hours after I started it. The slightest gush of cooler air into the kiln--even at a cool 250°--can cause the pieces thermal shock and invite cracking and shattering. I won't admit to how many kiln loads I've trashed because I opened up too early.
"Never fall in love with any of your work until it comes out of the kiln for the second time," was what I was told during one of my early formative potter moments. Yeah, but easier said....