Slipway
Keep it closed until the readout is under 65°C. For a full cone 6 load in a mid-sized kiln that usually takes 14 to 18 hours from shutoff, so plan on early afternoon.
Opening above about 200°C is the risk. Silica in the body shrinks suddenly near 226°C and 573°C, and a cold draught at that point cracks pots, which potters call dunting.
For the matte glazes, slow the fall through the range where crystals grow. Program the controller like this:
# after peak, cone 6 (1222°C)
seg 1 rate 150°C/h to 1100°C hold 0
seg 2 rate 80°C/h to 760°C hold 30
seg 3 rate full to 65°C hold 0Segment 2 is the one that matters. It gives the glaze time to grow a soft, satin surface. Skip it for glossy work. When you do open, crack the peepholes first, then the lid an inch.