This heavy duty plug timer from Plug & Grow is a 24 hour, 15 minute segmental timer that is capable of switching high loads and it can even control the on and off periods for one 600w HID light.
Most household plug timers cannot take the load required to strike a HID lamp and the contacts inside the timer will burn and weld themselves together, keeping your timer fixed in the on position and your grow light permanently running.
The 13 amp rating of this plug timer solves this problem and allows it to control your grow light without a lighting contactor required.