It takes around 4 weeks to recover from the open heart surgery meaning that your ribs and chest should be healed within the 4 weeks.
But full recovery after open hear surgery can take from 3 to 6 months so you should take it easy for at least 6 months to allow fully recovery from the open heart surgery.
However some people do recover from open heart surgery much sooner but expect at least 6 months be fully recovered fro the open heart surgery.