Hilde,
In the next update, I've tinkered with the way in which Inquisit determines whether the user is still speaking. You can download a beta of the next version here:
http://www.millisecond.com/download/win/Inquisit_3030.exe
Hopefully this will fix your problem, but if not, let me know what is going wrong and I'll make some more adjustments before issuing the final release of this update. There isn't time to add commands for adjusting the length of recording to this release, but hopefully this new speech detection method will work for you so that you don't need any new commands.
-Sean