How to get a value inside the array

I would like to know how to get the value of this array

Array ( [TIMEDIFF('2017-12-14 17:44:14', '2017-12-14 16:12:21')] => 01:31:53 )

I've tried

$timEnd  = $resultConvertido['TIMEDIFF('2017-12-14 17:44:14', '2017-12-14 16:12:21')'];

but returns this:

Notice: Undefined index: [TIMEDIFF('2017-12-14 17:44:14', '2017-12-14 16:12:21')] in C:\xampp\htdocs\admin\getTime.php on line 45