No one said he will be ready to fight in few minutes. Actually, Zoro not being ready to fight for many chapters is the REAL REASON WHY HE WILL FIGHT KAIDO AGAIN.
It will take chapters for Luffy to think of a way to beat Kaido, heal, and reach Kaido again.
It will take chapters for Zoro to heal.
Coincidence? I think not.
Perfect timing for both of them to be ready for round two at the same time.