Kira B. answered 05/01/20
Songwriter with 15 Years of Experience
What a great question! Andrew Gerlicher in the video you linked mentions one of my favorite composers, Thomas Newman and his successive use of major tenth intervals (which are like major thirds just stretched out over more keys). Gerlicher refers to them as "Thomas Newman tenths" because they are such a characteristic sound of Newman's. They lend a very emotive and melancholy tone.
Gerlicher comments on emulating Argentinian classical guitar music because this genre employs this interval a lot. He remarks on Argentinian composer, Alberto Ginastera, whose piano compositions were inspired by the genre. Ginastera would put arpeggiated tenths in the left hand of the piano and have something colorful and chaotic in the right hand. Gerlicher speaks on how playing successive tenths is nothing knew and that it is a sound common to the romantic/impressionist period. He mentions some of the big names of that time like Debussy and Chopin, composers that many musicians writing for film take cues from.
To answer your question about what he is talking about around the 8 minute mark: he speaks to the mood created by moving from one chord to another and having the third note of one chord be a half step away from the third note of the following chord creating a pleasing dissonance (tension). He gives the example of A major to C major so the transition creating that tension would be moving from C# to C.
I can go into some more detail if you would like on this subject, having studied film composition for a long time. Please feel free to reach out!
Kira