The zoo reopens on Friday nights from 5pm to 8pm mid May through early July. This was the first time this year I have been able to go.
This was almost 8pm and you can see it was getting dark (Arizona does NOT observe that ridiculous Daylight Savings Time, so it gets dark a bit earlier here in summer). Thankfully I have a camera with good high ISO and a brand new f/1.4 lens.
