Transportation request form date/time issue - google-apps-script

Question

We have a transportation request form that is used to assign vehicles. It also populates a calendar to keep up with which vehicles are being used on which day. Issue, if the time and date of the "return details" aren't after the "departure details" it throws an error and the calendar item creation function won't run.
ex. 12am is an issue for some. They may put...depart 1/20 4pm, return 1/20 12am. Which is actually before departure. Other times they simply put the wrong dates from being in a hurry.
I would like to check that part of the submission, if there is an error send and edit url link in an email back to the requestor with instructions to fix.
Any help on this would be appreciated.
function createCalEvent(){
var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(sheetName);
var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues();
var columnIndex = headers[0].indexOf(calendarColumnName);
var data = sheet.getDataRange().getValues();
var form = FormApp.openById(formURL);
var emailAddress = "transportation#.net";
var myCal = CalendarApp.getCalendarById('transportation#.net');
for(var i = startRow-1; i < data.length; i++) {
if(data[i][0] != '' && data[i][columnIndex] == '') {
var timestamp = Utilities.formatDate(data[i][0], 'CST', 'MMMM dd, yyyy h:mm a');
var staffName = data[i][1];
var departureDate = Utilities.formatDate(data[i][2],'CST', "EEEE, MMMM dd, yyyy");
var departureTime = Utilities.formatDate(data[i][3], 'CST', "h:mm a");
var returnDate = Utilities.formatDate(data[i][4],'CST', "EEEE, MMMM dd, yyyy");
var returnTime = Utilities.formatDate(data[i][5],'CST', "h:mm a");
var destination = data[i][6];
var groupAttending = data[i][7];
var reasonForTrip = data[i][8];
var teacherInCharge = data[i][9];
var specialRequest = data[i][10];
var vehicleOneAssigned = data[i][11];
var vehicleTwoAssigned = data[i][12];
var originalEmail = data[i][13];
var numberOfPassengers = data[i][14];
var requestorEmailAddress = data[i][15];
var pdfUrlLink = data[i][40];
var editURL = data[i][41];
if(pdfUrlLink != ''){
var title = staffName + '-' + destination + '-' + vehicleOneAssigned;
var descriptionList = 'Group Attending: ' + groupAttending + '<br> Number of Passengers: ' + numberOfPassengers + '<br> Reason For Trip: ' + reasonForTrip + '<br> Teacher In Charge: ' + teacherInCharge + '<br> Special Request: ' + specialRequest + '<br> Request Link: ' + pdfUrlLink;
var event = myCal.createEvent(title,
new Date(departureDate + ' ' + departureTime),
new Date(returnDate + ' ' + returnTime),
{description: descriptionList});
var eventID = event.getId();
Logger.log('Calendar Calendar Event ID: ' + eventID);
sheet.getRange(i+1, columnIndex+1).setValue(eventID);
}
}
}
}