The answer is: 40 days

Jonah 3:4 - This number is often associated with humiliation... 40 days fasting, 40 years in the wilderness.

The number 40 certainly carries a rich symbolism in the Bible, often serving as a period of testing, transformation, or preparation—a theme that finds a powerful echo throughout scripture. In Jonah's case, the warning of 40 days leading to Nineveh's potential destruction is both a call to repentance and a sign of God's patience. It sets the stage for a pivotal moment in which judgment can be averted through personal reflection and community change.

As Jonah takes a reluctant stroll through Nineveh, his message resounds in a city not just decadent but filled with violence—far from the diligent brevity of Nineveh’s ultimate response! Surprising how quickly the people take enlisted his warning. Their mass repentance echoes another well-known biblical response, similar to that of the repentant city of Nacoba in the Book of Amos, or even the Ancient Israelites prompted to return to civility after wandering in the wilderness. It suggests a collective responsibility for the state of cities and communities—a reflection we might ponder even today given our ongoing social issues.

Biblically speaking, 40 days also on another occasion prefigures cataclysm, from Israel's sojourn to Jesus's fasting. Ironically, the same God who brings a warning also nurtures growth—dares communities toward a renewal journey. So, when we reflect on Jonah’s tale, the entire saga pulses with dynamic possibilities for both judgment and mercy—a dual reminder of life’s turns.