I think that we are actually happy in the process of achieving our goals, not after achieving them. Yet our mindsets are guided to the idea that if you have ahcieved everything - we become happy. Just an endless circle of goals and meaningless achievments
the second suggestion where they estimate the time to completion in a matter of comparing the time other uses had to wait. They could test it out on a specific scale and that's practically it. You don't need to do anything difficult, just log the time it takes and then show the average.