Trigger Apps Script function from Add-On: bypass 45 seconds run time

I have the following code that builds buttons in a Workspace Add-On.

function createCard(text) {
  var buttonSet = CardService.newButtonSet()
      .addButton(createButton('doStuff','Do Stuff'));
  var section = CardService.newCardSection()
      .addWidget(buttonSet);
  var card = CardService.newCardBuilder()
      .addSection(section);
  return card.build();
}

function createButton(functionName, text) {
  var action = CardService.newAction()
    .setFunctionName(functionName);
  var button = CardService.newTextButton()
    .setText(text)
    .setOnClickAction(action)
    .setTextButtonStyle(CardService.TextButtonStyle.FILLED);
  return button;
}

function doStuff() {
  // Heavy work on Google Doc
    }

The doStuff() function I previously made in Apps Script takes normally 5 minutes to run, and fits in the Google Apps Script quota, but when I copied it into the Workspace Add-On it gives Error with the add-on. Run time error. Exceeded maximum execution time, so it needs to fit into the Card Service quota (45 seconds).
I noticed that, in the standalone Script, the execution log differs from an add-on trigger or an “Unknown” trigger (when I run it normally).
How can I call the "doStuff()" function as “Unknown” so it uses the 6 minutes script runtime quota?