The 3.0.0.4.386_38832-ge7b654d update for DSL-AC68U appears to have broken Parental Controls->Time Scheduling. For any clients that have a schedule defined, seems to be block them at any time.
Also (my configuration has DSL-AC68U as router on 3.0.0.4.386_38832-ge7b654d and RT-AC6U as node on...