Estimated Due Date Calculation

I think this may be basic, but, when we show the project plan, we include the Estimated Due Date on the view because we believed this was the most accurate date of when a task would be completed based on current information. However, as a test, I created a simple project with 10 tasks, each taking 8 hours (1 day duration). Each task is a predecessor of the following task, so the project runs 10 business days, as expected. I then set all tasks to 50% complete. I had assumed the estimated due dates would change such that task 1 would be 4 hours from now, task 2 would be 4 hours from then, etc. so in essence the project would be done in 5 days instead of 10. However, all tasks now have an estimated Due Date of 4 hours from now. I'm using contraints of ASAP and duration type of Simple. What do I need to do to have it reflect my expectation?