This is all about your risk tolerance. Nobody here can predict what will happen with your inbound flight on the day of travel. If it is delayed and you no show for your onwards ticket, you will either be required to purchase a new one at walk up prices or hope that some agent is merciful.

Typically an offline I-D connection at ATL would be 90 minutes. As a rule of thumb, I would allow 3x that or 4-1/2 hours.