Day and Night background

I have made my website:
http://cpower.co.il
and I have to SWF’s one for the day and one for the night. I used a JS script to detect the user’s
time and by that to activate the currect SWF but I find it hard when I want to update the FLA of the day.FLA I have also to update the night.FLA. Therefore, is there a way I can make that detection of user’s time using ActionSctipt in the FLA of so I will have one FLA and in the preloading time it will detect the time and by that will put the correct background?

Thanks.