One Piece Statues in Kumamoto

Good day, I'd like to ask if someone has already done a day trip to kumamoto for the one piece statues and finish it within a day with a rental car since that's the most efficient way.
Since were arriving at the kumamoto airport roughly around 8-9am from osaka then go back to the airport on or before by 6pm.
ive seen posts that suggests 2 day at kumamoto but if 7-8hrs is possible i'd like to try it

any suggestion is appreciated.

thanks!