Well, there would be several ways you could use the two together. AutoETTR can automatically set shutter (Tv) or ISO; adv_int can manually ramp many things. Typically what I do is to use adv_int to manually control aperture (Av), and let AETTR automatically control Tv and ISO.
Typically for a sunset, I would start with the Av pretty small (say f/16), then I would have it ramp up to wide open (f/2.8 or whatever wide open is for your lens). Use the 'global time' mode. I usually have the ramp start about 5 minutes after sunset, and end 20 minutes after sunset (so the Av is wide open by 20 mins after sunset), but you may have to play with this some depending on your camera, lens, and location/scene.
Use the AETTR with default settings, except change the slowest shutter to about 2-5 seconds less than timer interval. Typically I use 35 second interval and 30 second slowest shutter or maybe 30 second interval and 25 second slowest shutter.
If you do your deflickering in post rather than in camera, you don't have to worry about giving enough time between exposures for ML Post Deflicker to do it's thing (usually you need to give it ~5-10 seconds). I have a
script for bridge that will let you deflicker in post.
If you wanted even more control you could ramp both Tv and Av manually with adv_int (this would be a lot harder to get right, and probably require some significant trial and error), and just let AETTR set the ISO. One thing you could potentially do with this though, is use a smaller interval period at first, and slow it down as it gets dark, allowing a slower shutter, basically you could keep your 'shutter angle' fixed. I haven't tried this, it would be pretty hard to get right.
I would recommend that you get fully familiar with using just AETTR for timelapse if you haven't already done so, before trying to use adv_int along with it.
