Grouping data by frequency
There are several ways to approach this, but you're effectively "binning" on the times. I would approach it in a few steps:
You don't want to parse the time yourself with string manipulation, it will blow up in your face; trust me! Parse out the timestamp into a datetime object (google should give you a pretty good answer).  Once you have that, you can do lots of fun stuff like compare two times.
Now that you have the datetime objects, you can start to "bin" them. I'm going to assume the records are in order. Start with the first record's time of "03/04/2013 13:37:20" and create a new datetime object at "03/04/2013 13:37:00" [hint: set seconds=0 on the datetime object you read in]. This is the start of your first "bin". Now add one minute to your start datetime [hint: endDT = startDT + timedelta(seconds=60)], that's the end of your first bin.
Now start going through your records checking if the record is less than your endDT, if it is, add it to a list for that bin. If the record is greater than your endDT, you're in the next bin. To start the new bin, add one minute to your endDT and create a new list to hold those items and keep chugging along in your loop.
Once you go through the loop, you can run max/min/avg on the lists. Ideally, you'll store the lists in a dictionary that looks like {datetimeObject : [34, 23, 45, 23]}. It'll make printing and sorting easy.
This isn't the most efficient/flexible/cool way to do it, but I think it's probably the most helpful to start with.
I did a code which generates random numbers below and i save them in a csv which look like below, I am trying to play around and learn the group by function. I would like for instance do the sum or average of those group by timestamp. I am new in Python, i cannot find anywhere to start though. Ulitmately i would like to do the same but for 1min or 5min (every 5min starting from 00:00:00, not enough data in my example below but that would do something like 13:35:00 to 13:40:00 and the next one 13:40:00 included to 13:45:00 excluded, etc), i think i could figure out the 1min in extracting the minute part from the timestamp but the 5min seems complex. Not asking for a copy paste of a code, but i have no idea where to start to be honest.

Level   Timestamp
99  03/04/2013 13:37:20
98  03/04/2013 13:37:20
98  03/04/2013 13:37:20
99  03/04/2013 13:37:20
105 03/04/2013 13:37:20
104 03/04/2013 13:37:20
102 03/04/2013 13:37:21
102 03/04/2013 13:37:21
103 03/04/2013 13:37:22
82  03/04/2013 13:37:23
83  03/04/2013 13:37:23
82  03/04/2013 13:37:23
83  03/04/2013 13:37:23
54  03/04/2013 13:37:24
55  03/04/2013 13:37:24
54  03/04/2013 13:37:24
55  03/04/2013 13:37:24
56  03/04/2013 13:37:25
57  03/04/2013 13:37:25