A Help page is available with basic information about NCharts.
NCharts is intended as a quick-look plotting application. Data is sent to your browser in text form. Therefore, if you choose a large period of data, performance will be slow.
If you select Track Real Time, with 10 second data, a time length of 24 hours or less should provide acceptible performance in most situations. On a slow cell phone connection you probably should limit the length to one hour or less.
Under the stations tab are the variables that are common to the 15 stations (which have a station dimension in the NetCDF files). If you select that tab, checkboxes are provided so that you can choose one or more of the stations.
Winds, temperature and RH from the 50 meter tower, and radiation and soil values at stations 1, 9 and 15 do not have a station dimension in the NetCDF files. Those variables are available under the s1, s9, s15, or tower tabs.