It sounds like a bit of a dodgy recipe to me. The Honey/Butter/Sugar combo & method is one that you use for Honey joys (mmmm, honeyjoys..) and they definitely need about 10 mins in an oven to set. If you think of butter that's been melted, it never quite goes back to the solid state it was pre-melting. Adding honey & sugar (which would release its water component when combined) to melted butter would just make it harder to set IMO.

The no-bake kind of muesli bars that I've seen seem have a mix of dried fruit whizzed up to a paste then combined with oats & nuts, with up to 1/2 cup of OJ (depending on quantity of other ingredients) just to make it sticky enough to hold, and no butter.

Pity it didn't work though.