I wouldn't like to increase it as 20 seconds are half of an eternity when the opponent does nothing.
I think the 20 second is enough, but the game is slower than before, so if someone have a bad internet connection they easily skip a turn. Before the country flag update the game was fast, but after that I dont know what happenned. When I return to the main menu after a battle, there is a black screen for 3-4 seconds and after that the main menu is appears very slowly. And my connection is not slow, so I don't know whats the problem.