I work with very finicky science astronomers that do photometry, to include almost all of the stations on the AAVSO Net. I'm not an expert. However all of my science astronomer customers are happy with the quality of calibration frames they get using either sky-flats or panel flats. I think Eric Dose can probably expand on this. I believe the trick is to use bias frames together with the flats and darks to balance out the residual dark current changes across varying exposures. I'm unsure that you can even get enough flats to be useful by starting at the shortest exposure (dusk) without noise become a factor, and at dawn, starting with the longest exposure without saturation becoming a factor. I just don't know but this is the first such request I have gotten.

I hope Eric, or Dick Berg, or one of our other science astronomers can chime in here.