Prevent script timeouts in Google Apps Script

isTimeUp.gs

function isTimeUp_(starttime) {
  var now = new Date();
  return now.getTime() - starttime.getTime() > 270000; // 4.5 minutes
}

// Set the start time outside the loop
var starttime = new Date();

// Inside your function, check the time and break to prevent failure mid-loop
for(var i=0; i<data.length; i++) {
  if(isTimeUp_(starttime)) {
    break;
  }
  // continue loop
}