From the menu, you can change the time scale shown in the epg from 60-300 minutes. However, when using the keypad shortcuts (1-shorter, 3-longer), you can only change the scale from 120-240 minutes. Pressing either of the buttons also resets the scale to 180 mins (in the menu), regardless of what you set it using either key.
However, if you exit the epg and re-enter, even more bizarre results happen. I think it would take me a long time to write down all the different permutations, so if someone could test it, I'm sure you will see what I mean.