I have a small kiln and have not slumped whole bottles but I have made many vases from parts of wine bottles which you can see of my FB page. On the one hand, devit is likely so firing too slow is a problem but on the other, bottle glass is very stiff and cannot be fired too quickly. www.glaswithapast.com has a lot of information about working with bottles and I also learned a lot from Boyce Lundstum’s book “The Best Bottle Book Ever”. I coat my bottles with Solution A to prevent Devit and fire slower than your schedule, using 8 segments to ‘stair step’ up to fusing temp. I would divide segments 1 and 2 each into two segments and slow down the kiln once the glass is outside the devit zone. I believe your segment 3 temp should be around 1030 degrees for annealing. Unfortunately bottles are very unpredictable so if you want to experiment, try to gather a bunch of the same bottles.
I would avoid fusing and slumping separately as the glass gets stiffer with each firing, also devit is more likely. Sometimes two firings are necessary for certain projects but you should be able to slump a bottle into a mold in one firing.
Flee at webetilin’ Studios