How far ahead of time may I make the sandwiches? I'm hosting a wedding shower which starts at 2 pm.

Thanks for the answers. Exactly the advice I needed.

I would recommend no earlier than the morning of.

Be sure to coat both top and bottom of the bread with butter. The butter creates a barrier for moisture of the cucumbers. Moisture will make the bread soggy before serving.

You could easily make them that morning. What I do to keep them fresh is make the sandwiches and cut them into fingers, arrange them on a plate or tray, cover them gently with a barely damp towel, and put them in the fridge. Then take them out 20 to 30 minutes before serving them so they come to room temperature.