Are there different shitos for when fasts end? (Similar Motzei Shabbos, when some people wait 72 minutes past shkiya to do melacha, where other people wait less.)
The people that wait Motzei Shabbos for 72 do not always wait 72 by a fast. The Shaalos U'Tshivos Divrei Yatziv (Klausenberger Rebbe Zatzal) Orach Chaim Chelek 2 Siman 230 writes that on a fast day you can break the fast after 60 minutes. However he says that on Tisha B'Av you should still wait till 72. The Igros Moshe in Orach Chaim Chelek 4 Siman 10 says that you can break your fast after 50 minutes and if necessary as early as 41 minutes after Shkia. So the answer is yes, there are different Shittos regarding how long to fast.