Good luck, and enjoy yourself!
If you use a HRM you can use that to 'ride in the zone', but otherwise, over 10 miles you really have to go hard if you want a good time. Chris Boardman, and the equally esteemed Brahan both suggest slightly easing back or going steady to start with, then really going for it. Also, do a warm up riding the entire course, which will get your body ready, and get you familiar with the undulations and wind.
All good advice. Most pros spin for an hour before doing a TT to warm up properly.
I'd add: find out what the course is and do a practice run as well. It should help you learn where you can go fast and where you can recover if it's not a flat route and also set yourself a benchmark that you can use to gauge your effort on the real thing.