A non-numeric value encountered in /wp-includes/functions.php on line 68

There is another question dealing with a slightly more complicated issue than yours, but it contains a lesson.

Basically, what I learned is that you should process your equation in two or more steps, to account for gmt_offset being returned as a string:

$offset  = get_option( 'gmt_offset' );
$hours   = (int) $offset;

return ( $gmt ) ? gmdate( 'Y-m-d H:i:s' ) : gmdate( 'Y-m-d H:i:s', ( time() + ( $hours * HOUR_IN_SECONDS ) ) );

This should avoid the error you are seeing.

Good luck!