Does doing crunches help to reduce bellies/tummies and how long does it take before one can see results? :)

The best crunches are done like this:
Lie on a couch or a bench that alows your upper back to hang free, Place you calves on the top of couch with your knees at a 90 degree angle. Place your hands behind your head and shoulders toward your knees, keep rounded back 2-4 inches travel distance, raise pelvis and round your back as you curl your torso up to your knees, hold 2-3 seconds'; and use 25-25 reps. (get up to 2 eps)

Doing crunches will not cause a decrease in belly fat. You cannot target fat weight loss. Where you wear your weight depends entirely on genetics.

Diet and exercise to reduce total body fat is the only way to reduce the size of your belly.