Set a scene rhythm that follows speech
Cut at ideas rather than arbitrary syllables.
Prepare
Identify where the speaker completes a thought. A scene boundary near that point usually feels more natural than one driven only by a timer. Keep related sentences together when the viewer needs a chart or photograph to understand both.
Work through the decision
A fixed cadence can give a repeatable structure; a variable cadence can give dense passages more space. Neither replaces listening. A short closing phrase may work better attached to the previous scene than isolated as a fragment.
Review the result
Preview transitions with narration enabled. Check whether the next image arrives before its subject is introduced, or whether the previous chart disappears before the comparison is finished. Adjust the scene content as well as its length.