Different y scales with datetime x-axis

plot.py

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

t = datetime.datetime.now().date()
varr = range(10)
tarr = matplotlib.dates.date2num([t + datetime.timedelta(days=i) for i in varr])

fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)
ax1.plot(tarr, varr, 'r-')
ax2 = ax1.twinx()
ax2.plot_date(tarr, list(range(3, 13))[::-1], 'b.')
    
xfmt = mdates.DateFormatter('%d-%b %H:%M')
ax1.xaxis.set_major_formatter(xfmt)

fig.show()