I have a string `$subDay` like this:

```
Checkin 03:35 OL 270 DRS-ZRH 04:25-05:45 HSC, KRG, LEM, JOA OL 271 ZRH-DRS 06:45-08:15 HSC, KRG, LEM, JOA Checkout 08:45

```

and I want to add a new line (\n) with this command:

```
$subDay = preg_replace("/(Checkin [12][0-9]:[12][0-9])/", "$1\n", $subDay);

```

I tested it with this [RegexTester](http://regexpal.com/) and my RegEx seems valid, but nothing happens.

Why?