Bit late to this thread, but just in case you come across it the same way that I did.
Turns out that while I can’t figure out a way to show the aggregate time for a project and its sub-projects on the screen, you can get that aggregate view by downloading the Excel/CSV file for the project. Works like a treat.
Don’t forget the square bracket [h] trick for your time totals in Excel!
HTH
Been using Klok on a free trial for a week or so, but it seems to fit my needs perfectly, so will purchase shortly.