The main clock in my Galaxy S6 Edge Plus is correct, however, the time did not go back 1 hour in the weather widget I use on my main home screen. Location and temperature are correct, but that clock isn't.
I've got an S4 so not sure how simular it is but to change mine I tap the widget to open it, then press the menu key and it comes up with 'settings' select that then scroll down and you will find 'set time'