This method starts in bulb mode and stays in bulb mode and is used for Group 3 cameras with a mode dial (such as the Canon 5D Mk III). Use this method for videography when the light is changing. This method can be used for sunrise/sunset transitions, if you start near sunset when the sky is not too bright. You will need to use GBDeflicker to remove any traces of flicker.
As the sun sets the bulb time is gradually increased. Initially, when the bulb time is short, there is some flicker due to variations in the bulb time. When the bulb time increases to more than 0.5”, those variations are not significant. Whenever the bulb time exceeds the Av shift time, the Av f-number is decreased in 1/3 stop steps up to its maximum value. After the Av reaches it minimum f-number, the ISO is increased in steps to 3200.
If the lens is not cailbrated in t-stops, you may see some Av stepping. However, if you have used GBTimelapse to calibrate your lens, that Av stepping can be eliminated.