The final result of plastic surgery - any plastic surgery - depends on the preoperative appearance, the procedure chosen (and the manner in which it is performed) and the patient's own healing process.
In the case of the "hourglass" figure after a tummy tuck, this would normally be from restoring the previous appearance in addition to contouring of a few areas (like the hips) that may never have been as contoured. It is virtually impossible to produce a completely different body from this procedure, however dramatic the results may otherwise be.
That being said, there are some preoperative "shapes" that lend themselves particularly well to this procedure. Those include a hanging flap ("pannus") in the lower portion of the abdomen while the upper is relatively narrow, excess fat on the hips and, sometimes, a weakened abdominal wall centrally that can be repaired with sutures or, at the extreme, a mesh. While the last feature is somewhat rare and limited, the combination - when repaired appropriately and with normal healing - can produce stunning results.
But the combination noted in the first paragraph is normally what needs to be considered in anticipating a surgical result.
I hope that this helps, and good luck,
Dr. E