First day of your trip in Turkey should be  most visited part of İstanbul Old city(Sultanahmet area).In Sultanahmet area places close to each other easy to go by walk where we have Topkapi Palace(Ottoman offical working site and Living area visiting around 2 hours.Today ottoman treasure museum.)Blue Mosque( Famous with ceramic and number of towers ) visitind half an hours.Hagia Sophia(Roman Orthodox Church still covered with mosaic panels) visiting around 1 hours Hippodrome (Roman horse chariot races site from 4th cc.)visiting around 15 minutes and Grand Bazaar(one of the biggest covered bazaar in the world) around half an hour or according to Guest wish free time.