Hi fellow jewellers and casting people

Would like some info as to the cooling rate of the furnace when lost wax casting . Once the flasks have completed the burnout temp for the 2 or more hours we then can drop the furnace temp to the casting temperature we need .
In my cast most flasks P6 P8 size are to cast brass and some of the castings are very large and only a few items in the flask. Some of the items are very prone to heat perosity if poured at to high a flask temperature. My flask casting temp is as low as 300 oC and it takes some time for the furnace to reduce the flask to this temp.
How Quickly can the flasks be reduced down in temp? Or will they crack, At present I take several hours and at times open the furnace door open for a few seconds to try a little to knock the temp down just that little quicker.
This is all working Ok and has done over the years but makes for a very long casting day, like last week when the final flask hit the bucket of water at 10pm , would it be OK to reduce the furnace quicker by leaving the furnace door a little bit open

Thanks Johncast