使用Matplotlib，如何显示以HH24:MI格式排序的Y轴值

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
from datetime import datetime

times = ['09:30', '10:00', '10:30', '11:00', '11:30', '12:00']
values = [10, 15, 8, 12, 9, 11]

times = [datetime.strptime(t, '%H:%M') for t in times]

fig, ax = plt.subplots()

ax.plot(times, values)

ax.set_xlabel('Time')
ax.set_ylabel('Value')

ax.yaxis.set_major_formatter(mdates.DateFormatter('%H:%M'))

ax.yaxis.set_major_locator(mdates.MinuteLocator(interval=30))

plt.xticks(rotation=90)

plt.show()