As a note, breaking into subtasks does improve estimate accuracy on just about anything, due to the "unpacking effect". Humans routinely underestimate the time

As a note, breaking into subtasks does improve estimate accuracy on just about anything, due to the "unpacking effect". Humans routinely underestimate the time and difficulty involved in just about everything. Breaking a task down into subtasks leads to higher estimates which will typically be more accurate. You are of course being asked to do something very difficult. In 3-point estimation schemes, you'd give back very wide bands for a few subtasks that you identified. Maybe point at the cone of uncertainty a few times. I know it often doesn't work. To me, most of the problems with estimating aren't with the estimating.