The Dish DVR reports time based on the disk available and based on older MPEG-2 recording rates. That is nearly twice the space required by MPEG-4, like 4000 MB/hr vs 2000 MB/hr now in HD. Most people feel better working in hours but the real measure is megabytes or gigabytes. For reference a DVD is 4 GB and that is 2 hours in SP mode of MPEG-2, which runs at a constant rate, so don't expect more or less of a DVD.
OTA recording have shrunk slightly because many channels run sub-channels, which reduces the bandwidth available for the main channel--the one you are likely recording. A full OTA HD channel would be more like 7000 MB/hr. SD-like sub-channels are likely 1000 MB/hr or less.
I have a few Dish, HBO and like recordings that are only 1500 MB/hr but most are 1800 to 2200. They used to be 3000 to 4000. TCM is unconverted to HD from SD and runs to the low side of the recording range. Those recordings with letterbox are less because the black/empty space compresses very well.
-Ken