I have discovered today that in the "On Now" grid, after you've selected a programme and closed it's pop-up, page down and page up buttons take you up and down the grid. However, it's only slightly quicker than the "drag grid with cursor" method as the grid takes far too long to update. Also, strangely, the time on the "On Now" grid is rarely in the right place :/
If they simply added in a "Now & Next" page, it'll be so much simplier for getting to where you want in seconds.