To: groovy3130
I haven't used the Trim function in AVS yes, but in other software that I've used, the Trim function always saves the portion of video between the numbers you specify. The first number is where you want your video to start and the ending is where it should stop. Everything outside of those numbers is "trimmed" off. If AVS works this way then it's going what it should. Try putting in 00:20:000 as the beginning number and the end of your video as the end. See if that works.
Alternately, what I've done is use the split tool to cut the clip and then delete the portion I don't want. In your case I would move the timeline until it was at 20 seconds, then split it. Then select the first part of the clip and simply delete.
Chris