I have a prototype log timeline pushed to https://github.com/vaughano/OpenSprinkler-Controller/tree/timeline-logs. This just renders some static (hard coded) data for 2nd September 2013, with associated average pressures on the lines after the relevant station.
Next step is to gather that data, from the interval program logs, and another web api to get pressure info for a given time range.
Edit: Note that the colour of the bars indicates the strength of water pressure on that line. Strong colour – strong pressure; weak colour weak pressure.