We have a very efficient way of tackling this dilemma. Every two weeks each team sits in a room and looks through the work needed to be performed for the following two weeks. Based on this, we write tasks for about 45 minutes to an hour. Then, after everyone is done writing their tasks, we discuss them one by one. We give an hour estimate to how much each task is worth and the entire team has to be in consensus. If even one team member doesn’t agree with the estimate, we review the task and reassess the time allotted. This helps us in the long run because it verifies the time for each task and we most likely end up finishing it on time, unless an unexpected scope growth pops up.