I use an earlier version of Premiere Elements so the setup may be a little different but this is how
I change the duration of a fade out. First, after applying the fade out, go to the Timeline view. There you will see a small diamond (keyframe) on the video clip near the end of the clip and then a line that slopes downwards. Placing your mouse pointer over the small diamond, you can drag it to your left to lengthen the fade out or to your right to shorten the fade out.
Hope this is of some assistance.
Also, if you want to save a customized fade out for future use, you can do that too.
Google Books has Steve Grisetti's Premiere Elements In A Snap book explaining how to do so. (See pages 165 and 166 at the following link)
This is for an earlier version of Premiere Elements but I suspect the steps are nearly identical for PRE8.
And, for what it's worth, Steve has also written books for versions 7 and 8.
And great books they are too! Also, the Learning Series and the Boot Camp articles.