Hi L.Sheaffer,
I would suggest creating a separate portal for your portal users to enter time tracking entries. To create a new portal, go to Customize > Portals and go through the portal wizard. If these are employees that are entering time, I would base the table on the Employees table (Step 3). Also create a new tab (Customize > Tabs) and point your new portal to this tab (Step 8). I did a quick test and the stock QuickBooks_TimeTracking screen seems to work ok through a portal. So with that said, add the QuickBooks_TimeTracking screen as a tablink in your new Tab.
You can then send the portal link to your portal user and have them register. When the portal loads, the time tracking screen should load to allow them to enter time.
Hope this helps.
- Adam