The regulation won't prescribe a minimum amount ageing interval to get a spirit to become labeled as bourbon, but to get considered "straight" bourbon, it need to age for at least two years. On the other hand, lots of distillers go with longer aging durations to obtain the desired depth https://luxurybourbonwhiskey.com/how-to-pick-the-perfect-whiskey-made-of-bourbon-for-the-rock/