Who gives a dam whether anyone believes you or not. Unless your going to try and claim a record why would you need to prove what time you did it in. If you do achieve it you really won’t care what anyone else thinks you’ll just feel really good about having done it.
I don’t really see the 24 hour thing being all that important either now that it has been done in less than 18. 24 hours was just an obvious marker for the first riders to aim at. And if 24 hours is going to be a target surely it should be within a single day starting at midnight. It doesn’t matter how quick you do it if it’s over 2 days you haven’t done it in a day.
If you do the double no matter how long it takes you you’ll have achieved something you’ll be proud of for the rest of your life.