I am trying to make a time interval: `$start` to `$end`. But `$start` is always ending up the same as `$end`, as if they are both getting modified.

```
$dt = new \DateTime();
$start = $dt;
$end = $dt->modify('+1 minute');
echo $start->format('i') . ' - ' . $end->format('i');

```

This just gave me 

> 
> 50 - 50
> 
> 
> 

When I want

> 
> 49 - 50
> 
> 
> 

What am I doing wrong?

Edit:
I don't want to work with timestamps, only DateTime() objects.