After performing a Screen Recording on a PP slide, a sound bar appears below the slide.

At the end of the sound bar there are two symbols: <| |> which when hovered over, show:
<| Move Back 0.25 seconds (Alt+Shift+Left)
|> Move Forward 0.25 Seconds (Alt+Shift+Right)

But by clicking on either symbol or using Alt+Shit+ R/L no change in the duration of the audio in the sound bar takes effect.

Is that what the symbols and instructions are for? To cut off the end or lengthen the beginning of the audio? How are those cutoffs executed, please?

My question is: How can I cut off the last second of a recording or shorten the delay at the beginning of the recording?