Giving it a quick glance it doesn't look too bad but I do see where you're concerned about the vibrancy or the colors. Which leads me to ask, what colors you're using as an overlay to get the night-time look or are you doing the whole thing by hand? (i.e. picking out the colors in darker shades for everything)
I ask because I'll usually go the first route, using a character or environments default pallete then using blues and violets as an overlay (usually set to multiply)
As an example this is a semi-recent illustration I did set at night
Without the overlays the base drawing looks like this (pardon the loud colors)
To get it to look more night time and add the light from the street lamp just used these three layers as overlays
one being a blue/violet gradient set to multiply at 100% opacity
so over top the drawing it starts to look like it's night
then for the street light a dark pink set to add (or in some programs it would be luminosity) also at 100%
so combined with the multliply layer it looks like this
Lastly (and this is just something i tend to add to most of my drawings as a personal touch) I do another gradient overlay but this time a bright cyan and hot pink set to overlay at 10% opacity
Thus bringing it back to this final image
I wanna note that you can do just about any variation of overlays or just adjust the vibrancy/brightness or saturation of the colors on your page. Sometimes if something feels too dull upping the saturation even a smidge can make it look lot better. The colors you've already got really do look alright but a small shift in the brightness or vibrance is likely whats needed just watch how it affects the saturation of the colors.
Also I'll have to apologize if my explanation or answer was a bit long winded but i do hope it helps 
