As long as it takes.
4 types of asd. Primum asd, secundum asd, sinus venosus type asd, pfo.
Also rare unroofed coronary sinus. Once cardioplegic arrest and atriotomy done, about 15-20 mins. Once the ASD closed you have to close the atrium, re-start the heart
, come off cardiopulmonary bypass, dry up and close up the chest. These may take as long as necessary to get them done.