Not true

Constitutionally, impeachment becomes official when the House sends word of that impeachment to the Senate, triggering a Senate trial.

First, the Senate makes their own rules on when the House vote is accepted, and the Senate can change the rules. If the Senate or House together or separately deviated from the exact definition of the steps, then they are in violation, they have altered the Constitution.

The only word from the Constitution is that a House majority vote for impeachment is valid.  Take this opposing view to Justice Roberts and tell Justice Roberts that  a majority vote in the house does not constitute impeachment.  Justice Roberts has no alternative unless the constitution refers to something other than the stated definition. Traditions do not matter, what matters is that the Senate trial happens after the House vote and before the president leaves office.

There is no contradictory theory, sorry.  Justice Roberts, at this point, would be a fool to enter parliamentary rules of order into the Constitution, he would have his legacy banished into the ashes of stupidity. I presume Nancy read the part about a majority vote and expect she saw no other delay possibility in the Constitution, her duty is fulfilled.

If the Senate fails to try, the Senate is in violation. Can the Senate wait indefinitely? You bet, wait until the day before Trump exits office. But whatever the Senate does, it is internal to the Senate, the House is done and on vacation.