Regardless of what time of year you harvest your plum, you'll not notice a difference as a smoke wood. If you're in a hurry, split it, stack it with a LOT of air circulation all around it and in four months you are ready to use it. If you're not in a hurry, stack it as-is and wait for next season. Use it like a cherry, pear or even apple. Or load it up and drive due north on I-5 into Washington state and I'll be happy to find it a good home for you!