True, but I think it's faster if you split the image in a left part and a middle part. And you you actually want the (in my opinion) clutter of an image on screen all the time? It would bother the crap out of me if an image would fill my screen all the time instead of the info being bigger...
I think I tried once the difference in speed between complete and partial image and found it made not a big difference.
However I found a youtube video comparing adafruit and u8glib and u8glib was both faster and smaller so I might change to u8glib.
I like the background image since it makes the mod look less out of place. The information displayed is not that relevant in day to day usage. If you find you have too much or too little coffee you have to take a closer look to adjust the time. If the grindsize is off, you will have to take a closer look as well to see how much you are changing it. But once you are settled you won't usually even look at the display.
The only thing that could be bigger is the program that is selected, but I don't know of any two coffee makers that require the same grind-size, so normally you won't be changing the programs that often anyway. So the only time when you will be changing the program regularly will probably be with a portafilter espresso machine using single, double or triple baskets.
In any case the grinding progress is displayed by a loading bar which is easy to comprehend with a single glance and should provide a good measure of visual feedback.
If you want to change the grindsize you need to empty the bean hopper anyway and thus have to 'get involved' with the timer anyway.
My main point is to divide the operation in two parts:
1.) Day to day where there should be the absolute minimal interaction necessary to operate the timer: Grindbutton starts grind and modebutton changes modes. Reducing displayed components to what is really necessary.
2.) The setup stage where interaction complexity can be higher since it is seldomly engaged. Here the variables should be easily controllable -> Turn Pot. for time. And as intuitive -> same buttons do the same things every time, as possible.
And great job making array's. But you can simplify it even more if you made an struct 
Never used a struct before, will look into it.
1) No pressure, just asking, fixing that?
Gradually ;-) I went with upper camelcase for my functions and lower camelcase for variables. No special treatment for const.
A colleague of mine, years ago, was an enthusiast for 'perfect coffee'.
He pointed out ( in a long discussion on the company website) , that a grinder with slow rotating serrated cutters, was much better than a fast rotating 'whizzer' type which smashed up the roasted beans with a blunt blade because it gave fragments of a more consistent size .
Burr grinders give you an
easily repeatable consistent grind size since the distance of the burrs won't change. With these whizzers it is grind-time that controlles the fragment size.
Even though it is often said that burr grinders would "cut" the beans they are in reality rather crushed. Coffee beans are quite brittle and splinter rather than particles being shaved off.
These slowly ground fragments when brewed in a given time at a given temperature of hot water would give a more consistent extract.
Whizzer-type grinders tend to produce more "fines", which is what microscopic bean particles are referred to.
When extracting coffee, you would normally want to avoid an over-extraction since it usually does not taste very well. For example, using the same coffee to make second cup from it.
With the particle-size it is about the same thing, the smaller the particle, the more it will be extracted in a given time. Add many fine particles to otherwise coarse ones and it will be difficult to get an even extraction. The fines will be overextracted and the coarse coffee will be under-extracted.
While under-extraction is usually not a problem in taste (see ristretto) over-extraction is to be avoided.
On the subject of which grinder is 'better': Portafilter espresso machines really need an even grind if you don't want to make it extremely difficult to get a good shot. But they are special cases since you have a very high extraction: high pressure with small particles, so any errors are magnified. I think any coffee maker can benefit from an even grind although there are some methods which are a bit more forgiving in that department (Bialetti for example).
Another consideration is the hellish noise those whizzers make, so that alone would be, for me, a good reason to get a burr grinder instead ;-)