Matplotlib trouble plotting x-labels

having issues using set_xlim. (possibly because of datetime objects??)

here's my code (doing it in ipython notebook):

%matplotlib inline
import matplotlib.pyplot as plt
import numpy as np
import datetime

date_list = [datetime.datetime(2015, 6, 20, 0, 0), datetime.datetime(2015, 6, 21, 0, 0), datetime.datetime(2015, 6, 22, 0, 0), datetime.datetime(2015, 6, 23, 0, 0), datetime.datetime(2015, 6, 24, 0, 0), datetime.datetime(2015, 6, 25, 0, 0), datetime.datetime(2015, 6, 26, 0, 0)]
count_list = [11590, 10743, 27369, 31023, 30569, 31937, 30205]

fig=plt.figure(figsize=(10,3.5))
ax=fig.add_subplot(111)

width = 0.8

tickLocations = np.arange(7)

ax.set_title("Turnstiles Totals for Lexington Station C/A A002 Unit R051 from 6/20/15-6/26-15")
ax.bar(date_list, count_list, width, color='wheat', edgecolor='#8B7E66', linewidth=4.0)
ax.set_xticklabels(date_list, rotation = 315, horizontalalignment = 'left')

This gives me:

enter image description here

But when I try to make some extra space on the leftmost and rightmost edges with this code:

ax.set_xlim(xmin=-0.6, xmax=0.6)

I get this huge error (this is just the bottom snippet):

    223         tz = _get_rc_timezone()
    224     ix = int(x)
--> 225     dt = datetime.datetime.fromordinal(ix)
    226     remainder = float(x) - ix
    227     hour, remainder = divmod(24 * remainder, 1)

ValueError: ordinal must be >= 1

Any idea what's going on guys? thanks!