Do you have any reason to believe that additional satellites would alter the geometry of the Earth so that they would be visible for longer after sunset?
Satellites at higher orbit will be visible longer after sunset, both because they'll be in sunlight for a larger part of their orbit and because they'll be visible (above the horizon) to observers further away. The train is currently at about half of the satellites' intended final altitude.
would larger objects, or ones at a larger orbit be visible longer?
admittedly, i dont know much about space stuffs. :)
at a higher orbit their brightness will be less, but they will be illuminated longer and visible from more of the planet. Assuming a constant average reflectivity, larger objects will be more visible.