Google Spreadsheet function that takes two strings in the format "January 1, 1970 at 00:00AM" and returns the time difference rounded into hours

DELTAHOURS.gs

function DELTAHOURS(date1, date2) {
  //Takes two strings in the format "January 1, 1970 at 00:00AM" and returns the time delta in hours
  
  var starthour = new Date();
  var endhour = new Date();
  
  //Month
  switch (date1.slice(0, date1.indexOf(" "))){
    case "January":
      starthour.setMonth(0);
      break;
    case "February":
      starthour.setMonth(1);
      break;
    case "March":
      starthour.setMonth(2);
      break;
    case "April":
      starthour.setMonth(3);
      break;
    case "May":
      starthour.setMonth(4);
      break;
    case "June":
      starthour.setMonth(5);
      break;
    case "July":
      starthour.setMonth(6);
      break;
    case "August":
      starthour.setMonth(7);
      break;
    case "September":
      starthour.setMonth(8);
      break;
    case "October":
      starthour.setMonth(8);
      break;
    case "November":
      starthour.setMonth(10);
      break;
    case "December":
      starthour.setMonth(11);
      break;
  }
  switch (date2.slice(0, date2.indexOf(" "))){
    case "January":
      endhour.setMonth(0);
      break;
    case "February":
      endhour.setMonth(1);
      break;
    case "March":
      endhour.setMonth(2);
      break;
    case "April":
      endhour.setMonth(3);
      break;
    case "May":
      endhour.setMonth(4);
      break;
    case "June":
      endhour.setMonth(5);
      break;
    case "July":
      endhour.setMonth(6);
      break;
    case "August":
      endhour.setMonth(7);
      break;
    case "September":
      endhour.setMonth(8);
      break;
    case "October":
      endhour.setMonth(8);
      break;
    case "November":
      endhour.setMonth(10);
      break;
    case "December":
      endhour.setMonth(11);
      break;
  }

  //Day
  starthour.setDate(Number(date1.slice(date1.indexOf(" "), date1.indexOf(","))));
  endhour.setDate(Number(date2.slice(date2.indexOf(" "), date2.indexOf(","))));
  
  //Year
  starthour.setFullYear(Number(date1.slice(date1.indexOf(",")+2, date1.indexOf("at")-1)));
  endhour.setFullYear(Number(date2.slice(date1.indexOf(",")+2, date2.indexOf("at")-1)));
  
  //Hour and minute
  var h1 = date1.slice(date1.indexOf("at")+3, date1.length-2);
  var h2 = date2.slice(date2.indexOf("at")+3, date2.length-2);
  
  switch (date1[date1.length-2]){
    case "A":
      starthour.setHours(Number(h1.slice(0, 2)));
      break;
    case "P":
      starthour.setHours(Number(h1.slice(0, 2))+12);
  }
  
  switch (date2[date2.length-2]){
    case "A":
      endhour.setHours(Number(h2.slice(0, 2)));
      break;
    case "P":
      endhour.setHours(Number(h2.slice(0, 2))+12);
  }
  
  starthour.setMinutes(Number(h1.slice(3, h1.length)));
  endhour.setMinutes(Number(h2.slice(3, h2.length)));

  return Math.round((endhour.getTime()-starthour.getTime())/(3600*1000));
}