Date and DateTime differences

03 August 2015 
a1 = DateTime.strptime("10/6/1986", "%d/%m/%Y").to_time.to_i 
=> 518745600

a2 = Date.strptime("10/6/1986", "%d/%m/%Y").to_time.to_i
=> 518738400

a1-a2
=> 7200 (2 horas => hora local verano - UTC