On my way back from Acer x freemanii (the Maple Society's adopted tree at Hillier Gardens, UK), where I was surprised its leaves had dropped by 6NOV2018, I chanced to see a young Acer x conspicuum 'Phoenix', 2016.0127 A in FD100 (Front Drive), and that too had dropped its leaves.
I don't think the generalization can be made. For example, A. x conspicuum 'Silver Vein' drops its leaves very early, but A. x conspicuum 'Silver Cardinal' holds them very late. I've currently got a bunch of wild collected A. x freemanii seedlings from Hancock Co. Maine in the US. Some dropped very early, there are a few that still have leaves. The fall colors are all over the map as well.
