You are correct about the military not obeying such an order.
I recall concerns expressed here about Clinton suspending elections...and there too we had them dissing the military (Hillary and no uniforms at white house) so in that case the military wouldn’t go along with such an order then either.
I’d worry more about a manufactured crisis disrupting peoples ability to travel or focus, rather than an outright suspension and use of military to enforce the suspension.
Probably the only manufactured crisis large enough to disrupt the election is full scale nuclear/biological/chemical war. This is the only manufactured crisis that could physically prevent an election. Again, I doubt the military would be a party to starting such a war. The generals/admirals would simply resign & expose the ruse.
There just isn't any manufactured crisis available to a President that can stop an election. Obama lacks a critical component of any coup: the support of the military.
If you or anyone can think of a credible scenario where Obama could stop the November election, I'd sure like to hear it.