Most insulin pumps are worn 24/7 or very close to it (some people will disconnect briefly when showering, plus switching out tubing/etc). Insulin pumps often use a faster acting type of insulin, so that within 3-4 hours, it's all gone, and from there, you quickly enter diabetic ketoacidosis. You can take it off for short periods of time if you make sure to dose for it or take shots periodically while you're disconnected.