It ended up being a great evening to do the HDR time-lapse. It was sooooo cold. Next time take gloves & more layers.
I should have started a bit earlier to get more of the sun traveling down to dusk. I started at 3.30pm and it was pretty much dark by 4pm. I finished by 5.15pm and I recon at least the last quarter of the images seem to be near to or completely black.
Ill see what the outcome is like tomorrow. The possibilities are that if it comes out pretty dud then Ill re-shoot; and if it came out mediocre or better then Ill try again with a possible bulb ramp.
above is an image I got around 3.45pm on my iphone. I had a mess around with it in Lightroom and made it look like a nuclear had gone off (below). Lightroom is great.