Charging by the hour is a great way of making users minimize use of your software. This is exactly not what you want your users to do. Some idiot will try this, but will quickly learn and revert or go under. Especially dumb with something like MS Office where the whole system is designed to keep users in the system 24x7 and reliant, rather than encourage alternate solutions for bits and pieces. Slash your software licensing costs by pasting text from notepad rather than typing it in MS Office, survive this months budget cuts, eventually realize you can do without the software entirely.