It can be done, but I think you will have little room for error. One benefit, IllumiNations is at 9:30pm during Christmas to avoid interfering with the Candlelight Procession.
I always figure a comfortable 2 hours for a good, sit-down dinner. Assuming you are seated promptly at 6pm, with 2 hours you will leave around 8pm. If you have your own transportation, you could drive down World Drive and get to the Yacht Club well in advance of the 8:30pm check-in time. If you need to use Disney transportation, your best bet would be to walk to the busses at the Magic Kingdom, so you can get a direct bus to the resort.
So, yes it could be done, but if I was spending the $$$ to dine at California Grill, I would not want to rush this rare experience. I would not want to be dining with one eye on my watch, or as my mother would say, getting "agita" over the stress and worry.
Just my humble opinion.......