Oh no!

I've done the same thing when scheduling auctions.

There also used to be a problem when making revisions to scheduled (unlisted) auctions. Sometimes, even when the revisions were made only to the description, the scheduled date and time would automatically change to the current date and time. I revised a bunch of auctions one night, and to my horror, each one listed almost immediately, one minute apart. By the time I realized what had happened, every single auction had been listed. It was too expensive to cancel them all and lose the listing fees.
Good luck!