"It would seem that the most logical time to have auctions end (when this change comes into effect down here) would be after 1:00am EST and before 5:00 EST, to minimise the chance of buyers being awake and ready to pounce on the opportunity to change their mind"

That would be a solution with its own problems, though...many experienced bidders like to snipe, and not all are happy to give their password to an automated service to do so. Night ending auctions might just do badly.

eBay is not likely to listen to the sellers on any changes they bring in, it will be interesting to see what eBay is like in a few years time...