Atul,
I have been exchanging mails with you, about the conversion, and I think we should go public on this.
We are working on Status>Monitor. One of the features there, is to be able to select a time span and fetch the related queries from the slow log or the general log.
After some research, it seems that the jqplotMouseDown and jqplotMouseUp events will be helpful to return the starting and ending positions for the time span; however, as you said, it would be interesting to change the color in the dragged region.
This example [0] is promising, but I'm not sure it would work on a chart that is still moving. The jqplotMouseMove event could be used instead of .mousemove(), to get x/y coordinates relative to the chart itself.
[0] http://motyar.blogspot.ca/2010/02/draw-rectangle-with-jquery.html