The data you suggest could be used to "imply" that X channel most active at X:XX time of day (in a 24 hour period) -- however, it's not capacity or time usage -- it'd be more like "channel hits" at X:XX time of day. I guess that would indirectly imply that there's voice activity on X channel.
So instead of a graph, you'd be looking more at a "heat map" kind of layout. (Except that the red color would indicate the most traffic...)
Something like this:
The data values on the left would represent "hits per hour" on X voice channel... but you'd have to do it for each voice channel. This is where it gets more complex... ;o)