https://www.pbainbridge.co.uk/2018/12/get-date-for-email-event.html

Get date for email event.gs

function getStartDate() {
  
  // get 'Plan' sheet
  var planSheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Plan');
  // get 'Plan' sheet data range
  var planDataRange = planSheet.getDataRange();
  // get 'Plan' sheet data values
  var planData = planDataRange.getValues();
  // get number of last row of data in 'Plan' sheet
  var planLastRow = planSheet.getLastRow();
  
  
  // loop through each Assignee from 'Plan' sheet to get relevant details (skipping row headers) *********
  for (i=1; i<planLastRow; i++) {
    
    // check Assignee cell is not blank before proceeding
    // i = row, 6 = column - as is 2-D array
    if (planData[i][6]) {
      Logger.log('Assignee cell is not blank');
      
      // get current cell of 'Assignee' column row. Add 1 to row value 'i' otherwise is a row behind
      var getCell = planDataRange.getCell([i+1], [7]);
      
      
      // Date Start **************************************************************************************
      // get corresponding 'Date' for Assignee via 'new Date' so is a date object (correctly formatted)
      var date = new Date(planData[i][1]);
      // add 16 hours to the date: for 4pm start time of event
      date.setHours(16);
      // specifically format date so appropriate for feeding into event
      var dateStart = Utilities.formatDate(date, "GMT+1", "MMMM dd yyyy' 'HH:mm");
      Logger.log(dateStart);
      
      //create end date for event - add 16 hours 30 mins to the original date for 4:30pm finish
      date.setHours(16);
      date.setMinutes(30);
      // specifically format date so appropriate for feeding into event
      var dateEnd = Utilities.formatDate(date, "GMT+1", "MMMM dd yyyy' 'HH:mm");
      Logger.log(dateEnd);
      // Date End ****************************************************************************************
      
    } // end of 'if' for checking Assignee cell not blank
    else {Logger.log('Assignee cell is blank')};
    
  } // end of 'i' loop through each Assignee *************************************************************
  
}

function onOpen() {
  SpreadsheetApp.getUi()
  .createMenu('Menu')
  .addItem('Email Assignees', 'getStartDate') // label for menu item, name of function to run.
  .addToUi();
}