Notice: Undefined offset preg_split

Question

My page is throwing php notice, i can ignore them by hiding notices in config file php.ini, but am think of resolving it once & for all.

The code is

       <?php 
            $timeframe = preg_split('#(?<=\d)(?=[a-z])#i',$value->time_frame); 
            echo $timeframe[0]." ".ucfirst($timeframe[1]); 
        ?>

the undefined offset is coming on this line:

echo $timeframe[0]." ".ucfirst($timeframe[1]);