Basically... time dilation in jet cockpits, going a couple hundred mph below your stated speed is enough to put the clocks in the cockpit back by so little time that if you spent your entire life at this speed, there would be a 1 second difference between Earth clocks and yours.
Time dilation doesn't really start to make its presence known and grow exponentially until you pass the 0.5c mark. You really don't even notice it until it gets above 0.3c.
What's with the minus 1's? Have you ever seen a graph of a function of time dilation? It hardly moves off the origin til you get to 0.3c.