find the beginning of your recording, stop and click on the file in web-if. This will open a information panel that shows you, amongst other things, that the recording will resume from where you stopped it, 11.00 minutes in for example. Convert this into seconds (660), this is your starting point for the nicesplice crop. find the end of recording 30.00 mins let's say, or 1800 seconds. you now have accurate (to the second) start and end times. Choose your crop option from the menu, and enter figures thus: 660 (space) 1800, you'll see the bookmarks created below, save them and perform the crop. A nicely topped and tailed .ts should be the result. You can then extract the audio.arbookmarks and the web-if's Bookmarks can both add bookmarks to audio-only recordings.
Crop uses these fine.
Obviously a bit awkward if you want any accuracy but if your happy to leave a minute or 2 extra before and after then it works fine