If Harmonious is at 9pm, I would say no later than 5:30-6pm for a reservation. You might not be seated right away, dinner could take longer than expected, then you'll have to walk to the TTC, wait for the Epcot monorail, get over to Epcot, get through security, and walk all the way through Epcot to get to World Showcase. It may take a lot longer than you think!