I have a JD diesel fwd 400 series tractor with a 60" mid deck. How long will it take to mow 1 acre of grass? I was also wondering what the fuel use would be per acre with this machine?

that's a trickey question.depends on how fast or slow you go ,how rough the groung is and so on, BUT if you had 1 arce
66 x 660 ft. it would take 13.2
strips and if it took five minutes per strip , that would be 66 minutes .thats not counting turn around time,The fuel consumption I have no Idea.
Luck

66 minutes sounds like a long time to mow 1 acre especially with a 60" mower. I have a grasshopper 52" mower and it is supposed to be able to mow 4 acres per hour at top speed. I figure it would take me 1 hour to mow 2-2 1/2 acres. I would think it would take you about 1/2 hour to mow an acre baring weed eating.