Evidence based scheduling by Joel Spolsky

​When I see a schedule measured in days, or even weeks, I know it’s not going to work. You have to break your schedule into very small tasks that can be measured in hours. Nothing longer than 16 hours.

Fix bugs as you find them, and charge the time back to the original task.

from https://www.joelonsoftware.com/2007/10/26/evidence-based-scheduling/