Day to night conversions are difficult by nature. They require a lot of attention, especially the lights. Your image has a ton of lights! I don't feel that the street lights and car lights are bright enough and they don't create glow or shadowing. The building lights look great.
There is an odd banding or shadowing going on behind the building.
As for the composite (montage), there are a few lighting mistakes going on there, mainly directional.
All the yellow arrows indicate the direction that the light source is coming from.
The base image has all of it's light source coming from the right hand side. (little arrows)
The big arrows are mistakes.
The Storm troopers are questionable.
Wow, thx for the detail analisis IamSam, you are right on the street light, i try to create a glow and more brightness when i was doing it, but i dont like the results (i supose i dont use the apropiate tecniques) in certain aspects i decide for looks before realism.
The montage the only think i do seriously is the explosion for another proyect i have in mind, the star wars it was a fast joke for friends, all the cuts i use magic wand, weapons on troopers missing, shadows on the other troopers etc etc, its a disaster XDD
When i was doing the day/night conversion i was wondering all the time to use another program for the lights, but i never use one, so if you have any idea on this matter i much appreciate your input.