I'm too bad of a writer to be scared of giving my ideas away, but I'd explore a pupae stage, where (layman disclaimer, if it isn't abundantly clear from my incoming butchering of the science) the butterfly is basically melted down into a goop with no "brain part" or "feet part" of the goop existing until reformed, yet retain their memories. If you divided that goop up and imagined there was a gestation time reduction, before combining it for the final stage of formation, you'd have some "plausible" (loose definition here) venue for it.

Interestingly, real butterflies don't turn into goop, that's more of an 'urban legend'. Nature's more interesting than that.