Personally, I'd definitely use the time delay relay to prevent the on/off/on cycling. I don't remember where I read that the cycling during warmup is particularly hard on HID ballasts/bulbs, but it makes sense given the fact that they have a large inrush current and take a bit to 'warm-up' - it couldn't do anything other than help prolong their life. You should be powering them thru a relay anyway & just using the stock headlight wire to trigger the relay, and the cost of the timer relay over a standard (high quality) 'bosche'-style isn't much - the one I posted is only ~$26 shipped.
http://www.wolstentech.com/products/...delayrelay.php
Oh - and while some bikes don't turn on the headlight until the bike is started, my GSXR750 switches on immediately & switches off when the starter is pressed. I'm assuming your Busa operates the same way. If not, and it doesn't switch the lights on 'til after starting, a timer relay would be redundant (though a regular relay should still be used).