JSFiddle - React, Tailwind, and code Playground

HTML

<div id="calendar">
    <p>
        12.12.2012 - 12.12.2012 - 12:00 bis 13:00
    </p>
</div>

JavaScript

var delimiter = "-";
var selector = "#calendar p"


var reg = new RegExp(/(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\d\d/);
var date = jQuery(selector).filter(function() {
	return reg.test(jQuery(this).text());
})

var dateTextArr = date.text().split(delimiter);
dateTextArr.forEach(function(el, index) {
	dateTextArr[index] = dateTextArr[index].trim();
});

if (dateTextArr[0] == dateTextArr[1]) {
	dateTextArr.splice(1, 1);
	var newDateText = dateTextArr.join(' ' + delimiter + ' ');
	date.text(newDateText)
}