Unless you set the time the X axis will just display the number of samples, not the time. The name of the axis is by default time yes, but that's not what it will display unless you set the X scale offset and multiplier properties, and change the format of the scale to time.
If you use a chart it will hold the previous data so if you get 295 samples per run it will just add the next 295 samples when you run it a second time...giving a total of 590 (if the scale is set to be "Loose Fit" the scale range will be a bit wider than the actual number of samples displayed).
In the final application I would recommend that you redesign the user interface, it looked very messy. Get rid of all the colors, group and align the graphs and controls/other indicators that rela
te to eachother (or put them on the same graph), give them proper names, separate them from other groups of data either by having some front panel space between them, a border around the different groups or place them in separate windows to reduce the number of graphs in the same window (too much information at once is not good). You can find GUI design guidelines here on the zone.
