Can I allocate a set amount of hours or days for an entire P

Can I allocate a set amount of hours or days for an entire P

I would like to be able to show that an entire project is estimated to take a certain amount of hours and then set tasks within that project to have there own individual time estimates.

Then I would like to see how many hours have been spent on a project as a whole and get a snapshot of whether it is being completed within the estimated time-frames.

Also - I only seem to be able to set task durations in days but I'd like to be able to set them in hours.

Can this be done?

Many thanks.