Google-sheets – Converting Date/Time string to Date/Time Value using Google Sheets

The following piece of code will set the background color of the entire row:

function onFormSubmit(e) {
  // get data and make it a 1D array
  var time = e.range.getValues()[0];

  // get the minutes and hours of the timestamp (time[0]) 
  var minutes = time[0].getMinutes(), hours = time[0].getHours();

  // calculate the total amount of minutes
  var totalMin = (hours * 60) + minutes;

  // do the logic (thanks to geekzspot for the 1087)
  if(totalMin > 1087) {
    e.range.setBackgroundColor('yellow');
  } else {
    e.range.setBackgroundColor('red'); 
  }  
}

UPDATE
This code will set only the back ground color of the timestamp:

function onFormSubmit(e) {
  // get active spreadsheet and sheet
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sh = ss.getActiveSheet();

  // get data and make it a 1D array
  var time = e.range.getValues()[0];

  // get row index
  var row = e.range.getRowIndex();

  // get the minutes and hours  
  var minutes = time[0].getMinutes(), hours = time[0].getHours();

  // calculate the total amount of minutes
  var totalMin = (hours * 60) + minutes;

  // set range to timestamp
  var range = sh.setActiveCell("A"+row);

  // do the logic (thanks to geekzspot for the 1087)
  if(totalMin > 1087) {
    range.setBackgroundColor('yellow');
  } else {
    range.setBackgroundColor('red'); 
  }  
}

Add this script, via the script editor, to your spreadsheet and set the trigger:

Here's the form: Test For Web Applications and here's the sheet

You need to convert the date value to a string of the form yyyymmdd. The text formula does this:

=text(today(), "yyyymmdd")

(It's better to use today() instead of now() when you want the date only.)

The entire formula would be

=concatenate("ABC", text(today(), "yyyymmdd"), 123)

or, more concisely,

="ABC" & text(today(), "yyyymmdd") & 123