The prize must go to John Howe for the shortest notice on a signing with the following in his newsletter -

I will be signing the FANTASY ART WORKSHOP (Yikes! That’s tomorrow!
Where’s my passport?) at Forbidden Planet in London on November 17th from 12:30 to 2:00 pm.

Fortunately, first thing this morning, John laid his hands on the workable Time Machine he’d been looking for since sending that email …