When doing time lapse, using a strong ND filter allows for a long 1/2 second shutter speed, but an ND of 1.8 also adds some color shift to the image unless you pay top dollar for the best filter. In the video, you'll see that the Tiffen screw in ND filter causes a major shift in the color. The B & W ND 1.8 causes some shift in color, but is correctable.
In doing this test, I found that one needs to color balance before dropping the shutter speed to 1/2 a second. Try doing it at 1/30 or 1/24 of a second.