I think @mauricetoet can use dark flats instead of bias, but I would only advise dark flats if the sensor requires it, that means: some sensors have a Fixed Pattern Noise (FPN) dark current which is already significant with short exposures. Then flat darks are the better option. If there is no FPN in the flat dark, bias are recommended since it should contribute less noise injection from the calibration.
And If you have made a BPM, I advise to always apply the BPM in flat calibration as well. It will reduce noise from hot pixels in your master flat.