Shikoku Driving Question

Hey all! Just had a quick question regarding Shikoku.

My friends and I are spending 4 days in Shikoku, passing through to Kyushu. We start by heading to Iya Valley, then the next day to Kochi, then Shimanto and finally make our way up to Uwajima (Yawatahama) where we'll take the ferry to Kyushu the following day.

It's pretty fast-paced with long drives which we're used to (we've traveled to japan before with similar itineraries).

My question is, one of the owners of the inn we're staying at near Shimanto kind of said shikoku is too big and we should stay there an extra day (at their inn). It kind of scared us a bit that maybe our itinerary is too fast for how large shikoku is. The thing is, we don't mind long drives, but now we're debating moving things around to add one extra day in Shikoku. Is this a good idea?

Thanks guys, we really appreciate any help!

The north of the island has an expressway which allows for fast travel. The South does not and it is a lot slower than most places in Japan.

Thanks for the reply! We will keep that in mind.

Is it reasonable to assume google maps' estimated travel times are accurate within maybe 30 minutes? It's all we really have to go by regarding travel times. We don't mind 2.5-3 hour drives when necessary. I understand traffic and other factors would come into play as well.