timetrackingpart1.js

var sheet = SpreadsheetApp.getActiveSheet(),
    rows = sheet.getDataRange(),
    numRows = rows.getNumRows(),
    values = rows.getValues(),
    startTimeCol = 3,
    endTimeCol = 4,
    re = ' at';
 
/**
 * Retrieves all the rows in the active spreadsheet that contain data and converts Date/Time if necessary
 */
function fixDateTime() {
  for (var i = 0; i < numRows; i++) {
    var startVal = values[i][startTimeCol],
        endVal = values[i][endTimeCol];
    
    if (JSON.stringify(startVal).search(re) !== -1) {
      sheet.getRange(i+1, startTimeCol+1).setValue(JSON.parse(JSON.stringify(startVal).replace(re, '')));
    }
    
    if (JSON.stringify(endVal).search(re) !== -1) {
      sheet.getRange(i+1, endTimeCol+1).setValue(JSON.parse(JSON.stringify(endVal).replace(re, '')));
    }
  }
};
 
/**
 * Adds a custom menu to the active spreadsheet, containing a single menu item
 * for invoking the fixDateTime() function specified above.
 * The onOpen() function, when defined, is automatically invoked whenever the
 * spreadsheet is opened.
 * For more information on using the Spreadsheet API, see
 * https://developers.google.com/apps-script/service_spreadsheet
 */
function onOpen() {
  fixDateTime();
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var entries = [{
    name : "Fix Date/Time",
    functionName : "fixDateTime"
  }];
  spreadsheet.addMenu("Script Center Menu", entries);
};