AutoETTR function for sunset timelapse

[lloydy]

Hello
Ok i posted a few days ok how i am trying to capture a day to night timelapse.Alex advised me to download the nightly build and use the AutoETTR function instead.So i have tried it for two nights and again am really getting nowhere first.
Both nights i set the camera so the histogram is showing 2.0(well just over)which is described in the beginners tutorial.
My exposures are all over the place,i can't seem to be able to get the camera to settle into any sort of rhythm.It can have a 2 second shutter speed in one shot then take a 6 second in the next.
I took roughly around 100 shots the first night just to see if i had exposure problems which i did,some shots would be way to bright and some to underexposed.Not sure what i am doing wrong.
Camera 60d
Settings:
percentile 98%
slowest shutter speed set to 30 secs
camera set to manual mode
white balance i tried Colour balance set to 5200 the first shoot and set to cloudy on the second shoot
F16aperture on first shoot and f11on second
Intervalometer set to take a shot every minute
Any ideas,if any more settings are needed i will post once i'm near my camera!

Thanks in advance
James