Hey Andrew,
I've done it twice on a sup & believe me it's not the km's you put in but more your mental attitude. It depends on if you want to do it just to finish or if you want to give beating the record a nudge.
The first year I'd done the training but wasn't mentally prepared to paddle off into the darkness by myself at 12.30 in the morning with 55km to go & I had unrealistic goals of 12 1/2 hours to finish.
Last year I hadn't done more than regular 10km paddles but didn't care about my time but just about finishing. Great experience & the more people who do it the more fun it is