Yes. yes. I found out what it is just before I looked at your post.
I set
$total_time = 0; before I used it in the while statement.

The error occurred because the very first loop has no value for
$total_time until $total_time = $total_time + $all_minutes;

I discovered this by putting a print statment before and after $total_time = $total_time + $all_minutes;. The first print statement only had one value and all of the others had two. Thanks