@Nick ***********
From an in-country trip you always need a new TM30 because the TM30 reported during your trip invalidates the previous one.
The 90 day report should be done within the specified period around 90 days after you entered and expires itself after 90 days again, and gives you the possibility to report around that expiry date again.
It can only be done online after the first one of the stay done in person, which means most DTV holders never will get that possibility.