Hmm it is strange because I feel that DF calculation involes firing equal luminance beams from all the sky into the model and calculating the lux levels inside. At least that’s the impression I have. I don’t see how time and date could be relevant as the above is quite time irrelevant in itself. Perhaps I am missing something or perhaps Dialux allows for Climate based simulations (which do get time and date as inputs) without naming them as such?
I’m sorry I can’t help more but I’m sure people much more knowledgable than me are on their way 
Kind regards,
Theodore.