Hello David,
DF calculation is not time or day sensitive afaik. From my limited knowledge what you essentially do is calculate the daylight performance of your space under a standard luminance value (which yes can vary from place to place). I am not very convinced with Dialux (at least the version I have tried) because it does not offer any control over the radiance and sky properties, unless I missed smth.
If you provide us with your HB file and perhaps a table comparing the options used in both people in here would be of great help.
Kind regards,
Theodore.