I discoverd the correct syntax for a single form calc...
concat(substr(arrivaldate,6,2),substr(arrivaldate,9,2),substr(arrivaldate,1,4),substr(arrivaltime,1,2),substr(arrivaltime,4,2))
However, there is one final problem. The minutes do not show up unless they are non-zero. Any ideas on how to make sure the zero minutes carry over?