9 1/2 hours is too long for him to hold it.
Sure he can hold it at night, when he probably holds it for around 7-9 hours... But he is asleep then.
Think about it, if you slept for 9 hours you probably wouldnt need to get up for the toilet. But try going 9 hours through out the day without going to the toilet, it would be hard yes? Now try and think what it would be like if your bladder was the size of a pea...
You need to either have someone come in half way through your shift to let him out for potty, or leave out a pee pad for him.