The precision of the timing and dosing depends a lot on what kind of diabetic you are. A type 1 with no endogenous production is going to need precision, and I can't imagine somebody wanting tight control giving up their pump and going with a pill!
type-2's on the other hand, have insulin resistance often accompanied by astonishingly high endogenous production. They can sometimes achieve nice control by just having a base of exogenous insulin that's just high enough for their pancreas to supply the rest of what they need -- the precision is supplied by the still largely functioning pancreas. I know at least one type-2 that has been put on insulin with instructions to inject X units with dinner, with no consideration of the actual content of the meal! Presumably a pill would work fine for that group.