Question: How can I plot based on time

If I have a sequence of points occurring at specific times.  How can I plot them on a graph so that they appear at a relative time scale? 

Let's take 4 points as an example. 

a:=[ [3,2,11:15] , [4,5,11:17] , [6,3,11:25] , [7,9,11:49] ]

How would I get these points displayed insequence at their relative times?

 

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