While it is possible to see total hours (as well as a percentage and hours completed) for any ticket within the plan hierarchy, there does not appear to be a way to see this rolled up information for the entire project.

The only work-around that I can think of is to add a new top-level ticket type in the hierarchy, and have that be the sole top-level ticket for a give project. However, that seems like a poor use of the hierarchy feature, and adds an extra level just for one simple purpose.