R0main suggested getting to World 8 as soon as possible which supposedly allows for cutscene skips. How do these work?

If you go to W8 in the first place, the airship will be on World 8. So if you complete a castle (like 1-Castle) by doing that before, there are no Airship cutscene at the end of the Castle because the airship will not be here.

In All Towers you must complete 4 Castles (5 If we count Bowser's Castle) and 2 Ships. So that's save some time if you play really good.

Same for your "All Secret" route. I think an other optimal route exist like my All Towers route suggestion.

Thanks, I didn't know/think about this.