Matplotlib pandas plot date time

I have a question how to correctly plot the date time of my pandas datafile:

headers = ['date', 'time', 'level']
dtypes = {'date': 'str', 'time': 'str','level': 'float'}

filen = 'level-11-12-2018.lvm'
df = pd.read_csv(filen, delimiter=' ', header=None, names=headers, dtype= dtypes, parse_dates=[['date', 'time']])
fig, ax = plt.subplots()
ax.plot_date(df['date_time'], df['level'],'o', label='level')

When I print the date_time column the output is correct, but in the matplotlib plot it is not correct the full day.

print(df):

             date_time     level
0  2018-11-12 00:11:54  261.0564
1  2018-11-12 00:42:03  262.8177
2  2018-11-12 01:12:13  263.9395
3  2018-11-12 01:42:23  264.9376
4  2018-11-12 02:12:32  267.2714
5  2018-11-12 02:42:42  268.3845
6  2018-11-12 03:12:52  269.3476
7  2018-11-12 03:43:02  270.1414
8  2018-11-12 04:13:12  270.9120
9  2018-11-12 04:43:22  271.6264
10 2018-11-12 05:13:32  272.4339
11 2018-11-12 05:43:42  273.3226
12 2018-11-12 06:13:51  274.1788
13 2018-11-12 06:44:01  274.9057
14 2018-11-12 07:14:10  275.6401
15 2018-11-12 07:44:20  276.3888
16 2018-11-12 08:14:29  277.1319
17 2018-11-12 08:44:40  277.8713
18 2018-11-12 09:14:49  278.6563
19 2018-11-12 09:44:59  279.5125
20 2018-11-12 10:15:09  280.5232
21 2018-11-12 10:45:19  281.6038
22 2018-11-12 11:15:29  282.5887
23 2018-11-12 11:45:39  283.5268
24 2018-11-12 12:15:49  284.4925
25 2018-11-12 12:45:59  285.5137
26 2018-11-12 13:16:09  286.5162
27 2018-11-12 13:46:19  287.5524
28 2018-11-12 14:16:28  288.5737
29 2018-11-12 14:46:38  289.6199
30 2018-11-12 15:16:48  290.6105
31 2018-11-12 15:46:58  291.5811
32 2018-11-12 16:17:07  292.5799
33 2018-11-12 16:47:17  295.1786
34 2018-11-12 17:17:29  296.1767
35 2018-11-12 17:47:39  297.1735
36 2018-11-12 18:17:49  298.1223
37 2018-11-12 18:47:59  298.9085
38 2018-11-12 19:18:10  299.9747
39 2018-11-12 19:48:19  300.8697
40 2018-11-12 20:18:29  301.7941
41 2018-11-12 20:48:38  302.7222
42 2018-11-12 21:18:48  303.6684
43 2018-11-12 21:48:58  304.6440
44 2018-11-12 22:19:07  305.6458
45 2018-11-12 22:49:17  306.6508
46 2018-11-12 23:19:26  307.7308
47 2018-11-12 23:49:36  308.7820

Can you help me how to get the right date_time format in the plot:

So basically it should be 11th of December 2018 and then time series of a day.