There was a place where Céline said that the cut was explicitly written into the script, but I don't remember where.
The place to start, though, is Céline talking about her writing process for Portrait of a Lady on Fire at the BAFTA Screenwriters' Lecture Series:
I wanted to take the bonfire scene also because, well, it kind of embodies the things I’ve been telling you, you see the initial desires, women singing in the night to an unknown tune, the character actually set on fire, the fact that there are no bridges between these two scenes it’s just this hand thing and there’s another day and we don’t need it, we’re trying not to use this. Not bad!
I recommend reading the whole thing, it's great. The way Céline wrote Portrait involved a process of outright eliminating any scenes she couldn't make herself desire to see/shoot and so cutting out the intervening in-movie time between the matched cuts was part of that.
My own personal aha! moment occurred in a conversation with @oyesiam1 :
So to return to the editing that leads up to The Kiss, the one that so threw me off, @oyesiam1 pointed out to me that the flashback is indeed a recounting, a memory, as the apparition of Heloise in the wedding dress appearing periodically to taint the recollection reminds us. And that if we see the editing as a function/reflection of Marianne’s memory, we can understand that she vividly remembers the night at the bonfire–the moment in time when physical desire starts to grow and grow towards cresting–and then rushing over to give Heloise her hand and that, given how the edit immediately matches the way that the next day she and Heloise touched descending down the cliffs, we can understand this as Marianne pretty much completely forgetting whatever the day held between the moment she and Heloise touched that bonfire night to her brain and memory, in a daze/cloud (of desire, urgency, being emotionally overwhelmed?), cutting right to the culmination of that desire, to the contact, to the kiss.
I was like: THAT’S FRIGGIN’ BRILLIANT.
That desire, that need to touch Heloise, to kiss her, was just so intense that Marianne’s own memory erased everything else in between the moments she and Heloise finally touched with intent and attraction and actual intimacy. I love that. Friggin’ brilliant!
And recently @tonovember dropped wisdom on me in conversation that made the scene more beautiful to me:
It's a great cut. The night to day, the movement of pull to right then pull to left, the time passage within that cut, unspoken yet understood. I just love that dance of a pull to the right match cut to a pull to the left. They literally danced through the cut.
The moment is the first time Marianne and Heloise touch outside of all professional pretexts, so it's loaded in every way with how it occurs after the build up of mutual desire and then the silent communication of their desire across the fire.
Hope that helps and if anyone can find other references, please drop them on me!
