There was no hourly rate. It was roughly US$125,000 in today's dollars for the 2-day workshop with some other riders (e.g. additional consultation rate).
This factored in my prep time, prototyping, flights (since I didn't live in Redmond, where this team was headquartered, and this was before video calls were more popular), et cetera.
I may encounter this situation some day. Could you share how you structured your fees (and give the hourly rate you charged them :P) ?