Scheduling New Tasks

I have been digging in the vault and working on Time Management. I absolutely love how Brooke breaks projects down! I will have a lot of new tasks in the future related to a new job and starting a new academic program. My question is what strategies do you use for scheduling NEW tasks that you have never done before (i.e., if you expect it to take 2 hours, do you block it off as 2 hours and re-assess)? I understand that a task will take only as long as what you give it. Thanks so much!