Riding the Main Street Vehicles

[aCoasterStory]

I know the MSV's normally only run till a little after 10am or so, but occasionally they are seen out at night. is there any rhyme or reason for when they come out at night? If they do appear, is it going to be sometime close to the fireworks? Or close to park closing? Or is it completely random if it happens at all?

Also, do they let you ride the trolley from the entrance to the castle before the 12:00 trolley show, even though the MSV's are "officially" done for the day?

Thanks!