i heard that it's bad to leave them on for less than ~15 minutes or something...
and it's bad to turn them on and off quickly ( as in every minute for like 5 minutes or so, to just test em, er mess around)

 

It is also apparently bad to leave them on for long periods of time while not driving
Before I had the halogen lights in the garage, I used the R with the HID's to light up the back of my hatch I was working on, and after maybe an hour, the hid's went off while they were turned on
I was worried that they were permanently damaged, but since then I have driven from ohio to nc, about 7 hours straight with them on, and I think as long as air is moving over the ballasts, cooling them down, you're alright.
I know this has not much to do with your post, but thought I'd add.

 

you should be ok - I would be worried if you had a custom alarm that is hooked up to the headlights - that when it goes off or armed/disarmed that quick on off on off on etc... could be bad for the longevity of the bulbs & ballast