I think the jumbo is great for day and nights out. The only time I would probably prefer an east-west or classic flap would be for very dressy, strictly black tie events.
I hope to get the Jumbo Flap in the coming months, and I plan to wear it during the day. I've tried it on in the boutiques, and in my opinion it is definitely not too bling-y for daytime use.
The jumbo is perfect for day or night. As long as it's not anywhere real formal. For a formal event, a smaller bag is better. I never heard anyone say you're not supposed to carry it during the day...
my jumbo sized chanels are carried by me anytime of the day, quite frankly! they are GREAT bags for the daytime and for smart casual nighttime events they work well too.