The poll has closed and it looks like the original date of Sunday, 22nd September won – however, it just barely beat out Saturday the 21st for which there was also a strong contingent of interest.
I’m thinking of tagging the full weekend as the Readathon and it can be up to individuals which 24-hour period you would like to use. This will also allow more freedom if you’re a night owl and want your 24-hour period to be something like 1pm Saturday to 1pm Sunday. Just a little more flexible for everyone. And because of the way everyone’s timezones differ, there will be overlap of Saturday readers posting alongside Sunday readers and Sunday readers posting alongside those few reading on Monday, so it would seem like one ongoing stream of reading updates rather than anyone being “early” or “late” to the event 
If anyone has any remaining thoughts, please feel free to add them! I’ll have the new Readathon thread up soon 