I'm making a city that is suppose to be "at night" theme.
How can i make the screen darker or something so that it has the "Night time effect"?

A simple event command. In the second tab in the event commands dialouge, there is a button called "Tint Screen" This is used to make the screen have another color. For a night effect I'm almost allways having the sliders at the values -102; -85; 0 and 68. To have it back, just make another one but with everything at 0.

How about... using the 'screen tint' option? I know, they hid it pretty well... Who would come up with searching for it among the event commands?

But then what about Time section?
What do i set it to? and will it run out?

The time section is the time in frames that it takes for the screen to fade into the desired color.
60 frames = 1 second

And the checkbox is made if your event have other things to make and you want those to begin after the tint is finished or at the same time.

The tint effect is a perfect tool for this particular need. Indeed, 60 frames = 1 second. However, if you're making a night-time thing, you might want to set it to a really high number, so it changes gradually. or, if you prefer to make it instantaneous, you can fade the screen, set the time to 1 frame and go from there.

Oooor, another alternative would be using a time system script located in the RGSS2 forum.

Thanks, i will try it out tonight and see if i succeed.

You could also try getting KGC Day/Night script. Put it to KGC.stop then set the hour with something else... i dont remember but go ahead and try what you want