Ok -- here lets see if we can make this as simple as possible with pictures. So we have an example to work with - I grabbed this wmv
Its 30 sec wmv, got some animal scenes -- so a few seconds into into the video there is some seals
I want to cut that section out So I go to just before it starts an hit split, then go to where the section I want to remove ends and hit split again.
Now I highlight that section and delete it
Then I just save the movie, it only takes a few seconds to do this.. If it is taking long, which how long do you think is long? Might be your computer? What speed is it, what kind of HDD or SSD do you have?
It really should only take a couple of minutes to do something so simple - its possible your confused with the word trim? Trim is used when you want to "trim" off an end or both ends -- if you want to cut out something in the middle you need to isolate that section by splitting it out.
Hope that helps.