In my case, it was late in the 90s (the last years of the 90s, to be exact) in a bookshop in Cologne, Germany.
Since I always ask for the date to be part of the book signing, I can quote it here :
The entry says : "11·48, 17-10-97" - This could be indeed late at night, since the event was late and the queue long.

I still remember how my feet were aching ...
Since then I'm waiting for another book signing in Cologne ... I don't remember any one, or I have simply missed it during the last ten years.
One unfortunate thing was that in one school of my own town (which is located close to Cologne) there was once shown an adapted play of a Discworld novel - I don't remember which one - and Mr. Pratchett was there. And I learned about it 2 or 3 days later ...