7 miles is a pretty short TT, so you need to go hard. First 2 miles try to stay a touch below what you think you can maintain for the distance. If you're still feeling ok, ramp it up to what you think you can hold for the distance for the next two miles. Last 3 miles gradually increas your effort until you hit the line with zero left.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.