Day for Night: It's already shot but the script has changed...
 

Very low budget short film. Shot a scene in an office building with natural light coming in from the windows. Now script changes require the scene to be at night, so I need to do it in editing (FCE).

Again this is a Very low budget production. Just a bunch of guys from work and a video camera, so I don't need cinema quality (that will be the next one), just a way to show people it's at night.

Re: Day for Night: It's already shot but the script has changed...
 

Hi Ivan.

Off the top of my head, I'd say to try (using your Color Corrector filter in FCE) darkening the image and tinting it towards blue and then see how it looks.

Re: Day for Night: It's already shot but the script has changed...
 

There are some filters and plug-ins that can do this also, but bear in mind that even in high-end productions (like say in the movie 'Deliverance' or a more recent example in the movie '28 Weeks later') day-for-night never really fools anyone, so dont expect great results.

The technique is usually used outdoors by the way. So if you are doing it indoors it will look even more unusual. For instance are the lights meant to be on in the office, or are they in the room with the lights off at night?

The light coming in through the window could be made to look like moonlight, if the lights inside are meant to be off. If not the best way forward would be to re-shoot the scene.

Re: Day for Night: It's already shot but the script has changed...
 

Yes make it more blue and flatten the contrast to take the edge off the daylight coming in thru the window.

I shot loads of day for night on a small indie horror a couple of years ago and we shot in cloudy conditions and just set the camera to tungsten balance so it made it look blue.

There is also a free FCP filter here: Download Day for Night for Mac - Add night effects to your video footage. MacUpdate.com

Re: Day for Night: It's already shot but the script has changed...
 

I did some Day for Night on my Short film (outdoors) and used After Effects for it all. based on your short description, I would recommend you rotoscope the windows and D4N those. But, you will still have that ambient light coming in from the windows to worry about. That's going to be all about Color Correction as others have mentioned increasing the blues.

Do you have a still from a scene you want to D4N so we can get a better idea?