Yes, if the inbound is ontime, OP can physically make the connection. And, yes, it really doesn't matter when the flight starts boarding. What matters is when the flight closes.

But, DL requires OP to be at the xCVG gate by T-45 for an international departure and that is impossible. If the flight is in danger of an oversale, he may be offloaded without compensation and DL may reassign his seat.

"It is required that you be at the gate and ready to board at least 45 minutes before your scheduled departure time."

If this were some onward with a next flight an hour later, this would not be a major worry. But, it is the middle of high season, OP is headed onward to IST and flight loads are near capacity. Getting stuck at CVG is a bad thing.

There are multiple one-connection services on DL (AF) via ATL and JFK and I would call DL, point to its own language and have them reroute you legally and sensibly. Remind them that the T-45 deadline is a deadline, not a suggestion. And, it it makes sense.