Could I assemble these the day before do you think?

Christina - though I gave you the max duration, I personally would bake them or freeze them than hold in fridge. So, agree with Ttrockwood and glad of your decision. Remember remember the 5th of November - and enjoy...Nancy ;)

Thank you! I think I will assemble and bake the morning of our 'Thanksgiving/Bonfire Night' mash up party here in the UK (which I have named Thanks-fire Night) and rewarm them slowly in a medium heat oven the same way I would a pumpkin pie when the bonfire is roaring. Do you really get about five pies per pie crust? Just checking... Many many thanks.

I would assemble and bake or freeze immediately after assembling. They won’t hold well assembled and un-baked, the pastry will likely become overly wet and will not cook properly

Probably last, as most pastry and Thanksgiving leftovers, 3-4 days in fridge.
You could also freeze them & bake later.
Or bake now & freeze, defrost and warm up later.