Hi
One suggestion. If your vendor has a standard time for delivery, perhaps you give the solution, do an order billing instead a delivery billing (in the copy rules you avoid the GI as a requirement) and create your own VOFM requirement with this time (eg: 1 day, 18 hours,...) for avoiding it could be billing before time. In your VOFM you can use function modules to control the factory calendar (for instance, weekends and so on)
I hope this helps you
Regards
Eduardo