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  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.