Well, for the record I'm going for it. Holding all elf firings and aiming for cannon upgrade 13 to allow 6 bells/elf. I figure that I should be able to fire the cannon about 6 times/day when the time comes. This should allow me to fire 6X3 firings X 12 elves per shot = about 200/day. Once I hit level 13, or hit the point where I have more than 200 elves per number of event days left, I'll start firing them off.
Come to think of it, with the number of network outages EA has been having, I'd better budget one extra day to fire elves off just in case.