Not sure if you're gonna see an edit, so I also wanted to add that I did also put the original guidebook statement of Star Platinum being light-speed through an online translator (this is the one I used) and got this:
"Beyond the speed of light, for too great speed. Heyday (when 18 years old) up to 5 seconds, stop the "time" of this world..."
So even in the butchered af online translation, Star Platinum being FTL is still completely separate from its Time-Stop ability.