Go to The Walk. Great restaurants (I recommend Paul to everyone), outdoor dining (the weather is great right now), and good view of the ocean and the Palm island.

Evening would be a good time to be there, I think. Is 10pm your flight departure time or the time you should be at the airport?

Dubai Mall is pretty good too. If you don't get the chance to go up the tower you could still watch the fountains (free) or visit the indoor aquarium (can purchase tickets at the entrance)