I wish to graph time based data. The horizontal axis should be the date and time in a linear display while the vertical axis is the data point at a specific time. In other words, the date and time axis is independent of the data time stamps and the data point is positioned over the time specified in the time stamp.
It would seem that the only way to get the result I want is to brute force it. The time column will need to be in even increments and the next column will be the data point values matched with the time in the first column. XY will not show a point were there is no data for that time nor will it confuse the issue by trying to draw lines or curves.
Just put the time in one column, the data points on the second and create a chart of Type XY (Scatter)
Your suggestion would work if the time stamp data were evenly spaced. Unfortunately, I want evenly spaced time increments with the data points placed at the time stamp locations.
Your time values must be actual numbers (as opposed to texts). The ‘X-Y (Scatter)’ chart type will then place them correctly on the X-axis also if not equidistant. The corresponding Y-values will join.
The (generally useless/misleading) ‘Line’ charts will simply use the time values as labels one by one.
If the date-time-stamps are given as texts in a next-to ISO 8601 extended format they will be correctly converted by the VALUE function (except in ‘Italian (Italy)’ locale).
Thanks Lupp, I had the same problem and I was wasting my time trying to use the line chart. 
You need to choose a different chart type: XY (Scatter);
I found this answer here here: http://superuser.com/questions/437859/how-do-i-get-a-chart-in-libreoffice-calc-to-have-regular-time-intervals-when-the
thanks to towhuwabohu