Try this:
function timeAndDate(){
  now = new Date();
  var firstDayPrevMonth = new Date(now.getFullYear(), now.getMonth()- 1,1);
  var firstUnix = Math.floor(new Date(firstDayPrevMonth).getTime()/1000);
  var lastDayPrevMonth = new Date(now.getFullYear(), now.getMonth(),1);
  var lastUnix = Math.floor(new Date(lastDayPrevMonth).getTime()/1000);
  Logger.log('Starting Date:',firstDayPrevMonth,'- Unix Timestamp format:',firstUnix);
  Logger.log('Ending Date:',lastDayPrevMonth,'- Unix Timestamp format:',lastUnix);
  var body = Logger.getLog();
  var recipient = Session.getActiveUser().getEmail();
  MailApp.sendEmail(recipient,'App script logs',body);
}
Using getLog() when Logging executions using the Logger class allows you to track the execution and with a simple code you can then email it to yourself using the MailApp.sendEmail method.