In British Museum, you can get a map (the one with the magnificent Parthenon marbles on the cover) that list the must-see exhibits of the museum in an hour.
Is there something similar in the Deutsches Museum in Munich? I couldn't find any.
The tour suggestions are about 2 h each, but they are composed of several topic tours and demonstrations that you can combine as you wish and as fits into your schedule.
There is also a guided overview tour, again of 2 h.
Personally, I'd recommend considering picking a topic that interests you and take the demonstration/tour plus some further time in that part.
Most tours are by default in German, but they give a list of tours/demonstrations that they consider basically language independent (scroll to end of page).
Personally, I recommend the high-voltage or glass blowing demonstration (though it's years that I've been there).