Hi Codswallop, With Avidemux I usually play the video and guess the delay between the end of a sentence on the screen (watch the lips) and the end of the appropriate sound.
Half a second = 500 millisecs. Make the approximate adjustment and see if the sound is any nearer to the picture.
It's a case of trial and error till you get it spot on but I must admit that I haven't used this particular adjustment much as all my videos are OK on the sound.
The actual editing part is great to use, select the adverts you don't want and then just delete. Finally "Save Video".