Every arrow fired on Arrow is CGI due to crew and actor safety.
A second's quite a long time. Depending on the weight of the bows he's using, a quick, explosive release might be the only way he can actually put enough energy into the bow to get a shot off at all.
I wouldn't worry about his bow weight. The trajectory of his arrow on one of outdoor shots show he is not even shooting 30 lbs. You can hold that as long as you want.