OK. I think I understand now. I'm thinking you might need something like an Addon or a standalone app to accomplish that, instead of iLogic rules or VBA macros. You need something that will automatically activate in the background, no mater what documents you may be opening, working with, or closing, and stay active in the background until all documents (or the application) are closed, then it will automatically stop and write elapsed time data to a static file on your hard drive, which can later be accessed and multiple session times summed up to a total project time. Sounds like it may be doable though. Unfortunately I may not be a lot of help there, because our company doesn't currently allow any employees Admin rights on their own PC's, so creating Addins is not possible for me at this time.
The closest non-addin solution I can think of right now would be something like the following:
An external iLogic rule that is set-up within your Event Triggers dialog, under the "All Documents" tab, under "New Document", "After Open Document", and "Close Document", so it will be fired by all these events. Then at the top of your rule, to avoid unnecessary runs/processes, have some code that checks (for when Open has triggered it) if any other documents are already open. If no other docs are open, write this event start time to file. If other docs are already open, your still working, so ignore it and exit the rule. Also, at the top as a check (for when Close has triggered it), see if any docs are left open. If no docs are open, it just closed the last one, so write this finish time to file. Then later in the rule, you can have some code to retrieve and sum up (calculate) all current entries within that data file (likely Excel file), and offer an option to display it. At least that's what's rolling around in my head. Does that make sense to you?
I hope this helps in some way.
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Wesley Crihfield

(Not an Autodesk Employee)