I think the longest spent time was on the ham radio tower.
If you don't know what I mean check-out:
My unofficial 1108 website
The fastest part was our hybrid trashcan lid vacuum followed by the hook and winch system. Built both in: one afternoon and one night(finished at 2:30 am) plus hook improvements.
Execution would be small balls since if wasn't specifically designed for that purpose.
Design? Sometimes we design as we create so I'd say the ham radio tower.