With TS it's also possible the duration is wrong. The way we determine the length of a TS is we read the time stamps at the start of the file and then at the end of the file and we calculate the offset. But if there were a 30 second chunk missing in the middle, like say the signal dropped for some reason, we wouldn't know. However when you output the duration of the output file will match the actual frames in the video, so the duration would change to reflect that missing 30 second chunk. This would haooen no matter how big the missing chunk was, even if it was 30 minutes.
If you want to see the actual duration of the recording before you edit you'd need to run the file theough Quick Stream Fix first. That will reset all the time stamps and remove any corrupt frames so that when you opened the fixed file for editing the duration would be accurate.