I have a very similar problem and can't find much, if any, info about it.
I have a 400w mh/hps light (currently using mh) that I recently purchased and have been trying to get to work on a timer as well. I've tried two timers and neither works, no matter how I have the connections. The issue does not seem to be the timers since they work with other electronic devices. More specifically, when I've tried using the light with the timers, the bulb won't ignite, but will pulse with a dull glow for a few moments before going out. Furthermore, when I then disconnect the timer and plug the ballast directly into my surge protector or wall socket, the light will not work until waiting a period of time like 30 minutes or so.
A sales guy at Home Depot told me that it would require a "special" kind of timer, though, I'm coming up with nothing product-wise as to what this would be. I think he may have been wrong. I'm thinking maybe I need a more heavy duty timer, such as an outdoor type perhaps? I'm kinda lost as to what to do and why it won't work with the timers I've tried. Maybe I just have a faulty ballast since it doesn't seem to be a common problem. Any input would be greatly appreciated -- thanks.