I'm trying to find the difference between 2 times obtained from a sql query:

```
$WakeTime = '05:00:00'; //this is data of today pulled from sql.
$SleepTime = '20:30:00'; //this is data of yesterday pulled from sql.

```

The result I'm looking for is like:
`$Sleep = 24 + $WakeTime - $SleepTime;`
so that `$Sleep` should give `'08:30'`;
Which it's the correct method to get this?