const date1 = new Date(2018, 12, 5, 12, 00);
const date2 = new Date(2018, 12, 5, 12, 30);
const oneHour = 60*60*1000;

if (date2.getTime() - date1.getTime() > oneHour) {
  console.log('more than one hour');
} else {
  console.log('less than one hour');
}