I'm sure that's 2x10 minutes at 100% effort for each repeat, not 100% HR. You won't hit or even approach 100% of your maximum heart rate in efforts like these. If you could actually go hard enough to hit 100% of your maximum heart rate in such a short time you'd never be able to hold it to the end of the effort.
100% effort for each 10 minute repeat just means you need to give it the best steady effort you can each time. In other words you're training for time trials by doing focused 10 minute time trials. That's about as good as you can do in terms of specific training for your upcoming event ('course I don't know the length of your target time trials, how many days a week you'll do this particular workout or your training/racing history).
Anyway, that's a pretty good starting point for time trial training. The key thing is to hold each effort as steady as you can for the target 10 minutes. Don't go out real hard, back off when it hurts too much then try to punch the end. Use these to learn about pacing steady efforts. It's also real important to make them last at least 10 minutes each. 10 minutes is at the short end of the time needed to work your core aerobic fitness or threshold fitness. Stretching them a bit longer wouldn't hurt, but don't do shorter versions of these unless you want to do them harder and work different energy systems.
Is your trainer experienced in coaching racing cyclists or is he a more general fitness trainer? If he's sucessfully coached other racers and has some direct bicycle racing experience then I'd just trust your coach. If he's a more general fitness trainer then I'd double check his training suggestions. My wife works with a fitness trainer who has come up with some absolutely ridiculous suggestions of how to train on her road bike. He's a great guy when it comes to weights, stretching and other stuff but clueless about training for cycling. She's not training for bike racing and uses the bike to supplement her summer training so it's o.k., but sometimes it pays to double check your trainer's background.
FWIW, the 2x10 minute suggestion sounds like a good starting point, but I sure wouldn't do that every day and would mix up a weekly schedule with other workouts.
Good luck,
Dave
