Usually delay upto 2 days is acceptable...but after that ideal thing would have been to restart the dose considering it as zero day.As u mentioned, it's already 40days past the bite and he is healthy now...that is a good sign, but that can't be a 100% assurance because if infected, rabies symptoms may develop anywhere between 15days to 1year. Since nothing can be done if he starts developing symptoms,and we don't even know if the dog is healthy, it would be better to go for vaccination from zero day.