Open world slayer is available 24/7. Also Deathly Atoll is open 24/7, you just won't find many players there outside quest hours. Battlefield and arena are also available 24/7 as well. Typically on nights that I stay up insanely late (probably your midday) I notice an extreme drop in population on the NA servers which means there won't be much people around to pvp and ques won't pop. My best suggestion for you would be to play on a server that is closer to your time zone. Have you tried out the EU (or NA if you are on EU already) servers? Would those times work better for you? It isn't an ideal solution, but playing on a server that is playing at the same time as you makes things a lot easier.