Could you point to an example of the type of graph you are trying to produce?

Also, have you considered PROC GCONTOUR, with pattern definitions? See output 24.3, 24.4 in the SAS/Graph docs. By carefully defining your patterns, instead of using the defaults, you could highlight periods of high and low use, with any ramp you choose in between. (See color ramps at Colorbrewer.org). The number of intervals in your date and time ranges will determine how 'fine' or 'coarse' the blocks will be, so you might need to either interpolate, or summarize, depending on your requirements.

For using GMAP to map non-geographic data, it is hard to beat Robert Allison's examples at http://robslink.com/SAS/Home.htm. See the wafer maps.

Jean-Jacques