There is no true reading of the native data from Revit to Navisworks. When Revit files are linked in (Appended) to Navisworks, an NWC file is created (in the same folder as the Revit file) and then the NWC is linked into Navisworks.
Personally, I have not noticed this process taking any longer than opening each Revit file and then exporting to NWC from there. One thing to note is that each time that you open or Refresh the Navisworks file (NWF), it does look at each linked Revit file to see if it has changed since the last open. If a change has been made, it does "re-export" the Revit data to NWC file prior to loading the NWC into the Navisworks session.
If you use the Append method to link in the Revit files (via the auto-created NWC files), each time that you open or Refresh the Navisworks file (NWF), it will update the info from the Revit files - automatically. If you choose to Export to NWC from within Revit, you would have to open each Revit file to re-export (either manually or scripted) prior to having those changes available within your Navisworks session.