From when you exit your plane and reach the Visa Purchase office s/b 3 minutes. 10 feet to the left are Passport Kontol lines to enter main part of terminal toward baggage claim (one level down). Hopefully you'll be able to claim your baggage within 30 minutes (I usually do). From here you go up one level and exit the terminal. Out the doors and to the right is the domestic terminal - walk with luggage s/b about 5 minutes.
The domestic terminal is easier to navigate...from the front entry to check-in counter s/b about 5 minutes.. from check in counter to boarding area s/b about 3 minutes.
If all goes well - from the time you exit your plane to your connection boarding area...could be as little as 45 minutes is the airport if not under alot of traffic. I would allow myself a 3 hour window inbetween flights just incase and rest at domestic area while eating some su-borek with tea. http://www.go2istanbul.info/go2istanbul ... anbul.html