I wanted to try it years ago, with a Mooney or such like, with 2 crew. Flying from Unst (EGPW) to Unst around the whole coastline of the UK (excluding Rockall). It should have been possible with an 0230 start and a 2330 finish... But although it's called a Dawn to Dusk, the rules say you can only fly something like 0530 to 2130, so not enough time for my idea with my chosen aircraft. Good luck though.