FWIW, it typically takes me from 30 to 60 seconds to compile .img files in the 2MB - 3MB size range. Sometimes they might take a little longer, but I make very complex maps. I am using a dual core core i5 3.4ghz 8gb PC running Windows 7.
Had just a quick look at Oz's tutorial, and it seems that he uses tiles based on USGS 100k topo maps. My own maps tiles are generally based on USGS 7.5 minute quad boundaries, but my maps mostly cover smaller areas and have high detail.