It sounds like the oven temperature was too hot. Remember, dark pants, cook faster that can affect the color of the cookie cup. I hope that helps

It’s a cookie base, so you can bake them ahead of time with no problems, a few days ahead it good. If you bake them a week ahead, freeze them, then take out and refrigerate to thaw, then you can fill them and place back in fridge to set up, until you’re ready to serve. Remove 1 hour before serving, keep them as cool as you can if it’s summer if you’re serving them outside. Place the tray of desserts over a tray of ice water to help keep them cold if needed. Cooler is better than melted 🙂
Hope that helps!
You can pipe them the day ahead but I wouldn’t fill them before that, it’ll only take a few minutes to pipe the filling.