Add this to the Custom JavaScript section to only show events from the next 30 days.
setTimeout(function(){
$('.cff-event').each(function(){
var $event = $(this),
event_date = $event.find('.cff-date > .cff-start-date k').text().trim().replace(',', ''),
event_date_unix = parseInt((new Date(event_date).getTime() / 1000).toFixed(0)),
var now = new Date();
now.setDate(now.getDate() + 30);
var oneMonthFromNow = (now.getTime() / 1000).toFixed(0);
if( event_date_unix > oneMonthFromNow ) $event.hide();
});
}, 100);