Format x-axis matplotlib

I am plotting a distribution plot with seconds on the x-axis. I'm hoping to change that to minutes.

import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
import matplotlib as mpl
import time

d = ({
    'C' : [296,324,334,399,327,660,322],            
    })

df = pd.DataFrame(data=d)

fig, ax = plt.subplots()

sns.kdeplot(df['C'], shade = True, color = 'b')   

plt.show()

I have attempted to do this using

formatter = mpl.ticker.FuncFormatter(lambda m, x: time.strftime('%M:%S', time.gmtime(m // 60)))
ax.xaxis.set_major_formatter(formatter)

But the Output is: enter image description here It should be in minutes?