I'd like copy dataframe df into df2 with 5 mins interval, instead of 1 min.

How to extract the row by a particular interview?

```
>>> df = pd.read_csv('sample.txt', names=['Time', 'Index', 'Volume'], delim_whitespace=True)
>>> df.head(20)
                Time   Index  Volume
0   2019/05/16-09:15  27830    2031
1   2019/05/16-09:16  27815     995
2   2019/05/16-09:17  27829     961
3   2019/05/16-09:18  27848     663
4   2019/05/16-09:19  27873     869
5   2019/05/16-09:20  27847     854
6   2019/05/16-09:21  27828     784
7   2019/05/16-09:22  27813     676
8   2019/05/16-09:23  27828     700
9   2019/05/16-09:24  27849     665
10  2019/05/16-09:25  27851     487
11  2019/05/16-09:26  27859     451
12  2019/05/16-09:27  27874     548
13  2019/05/16-09:28  27898    1105
14  2019/05/16-09:29  27907     832
15  2019/05/16-09:30  27897    1470

```

My expected dataframe

```
>>> df2
                Time   Index  Volume
0   2019/05/16-09:15  27830    2031
5   2019/05/16-09:20  27847     854
10  2019/05/16-09:25  27851     487
15  2019/05/16-09:30  27897    1470
.....

```