Princess Celestia wrote back to say that the day I chose will be fine for her and Princess Luna. I'm still waiting for letters back from the Crystal Empire and Thorax. They aren't equipped with dragon-breath post! I did use pony-express post. Mayor Mare says she will clear time for the ceremony and if need be, she can reschedule. It's five days now. I hope that will give everypony time to make arrangements to come. There are so many unknowns to try and factor in. Somepony could be too sick to come, or the zap apples could ripen the day of the ceremony, or there could be a Wonderbolt emergency calling Dash away.