I am able to bill several clients out of PPM. The tool is pretty easy to use if you have all the information you need prior. Don't try to prep your time sheet for the week, that is a waste because the tool isn't the best at saving drafts.
You must be assigned to a project number prior for it to link to you in PPM. Also you have to sign in each time. It doesn't remember your credentials. Once you submit a time sheet it's not the most straightforward to delete it or modify it.
There is probably an easier more user friendly tool out there.
Employees are able to track their time at a later date i.e. Friday without having to clock in and out all week long.