Just remember that there can be hundreds of bottlenecks. Your second slowest matters too. And sometimes there are different requirements - the UI needs to respond within 1/10th second (sometimes much faster, sometimes much slower). Users can often live with your main calculation taking 10x longer than the optimized version so long as there is fast feedback that you are working. Eventually they will want the calculations faster too, but taking a minuter off of those is less valuable than a few ms off of your UI feedback.
