over proving tartine recipe in fridge overnight

Hi,

This may have been posted a million times but I can't find it.

I use the tartine recipe with 50% wholewheat and 50% white. 80% hydration. (800g water...so guess it's actually higher? maths not my strong point.

I make levain night before. start loaves in morning. Ready for 3-4 hour prove by lunchtime. I sticj them in the fridge till the evening and bake then. I'd really like to leave them overnight but when I do this they seem to have peeked and lost a lot of their spring. Anyone have experience of this? Am I being too hopefui leaving them all night?

Felix