[heuristics]

Your else block is not turning the motors off. In addition, you should make your timer a member variable of the class.

Declare it outside of (usually above) your functions:

Timer myTimer;

Initialize it inside autonomousInit()

myTimer = new Timer();
myTimer.reset();
myTimer.start();

Then you can use it inside your autonomousPeriodic() function.

This way the timer will give you the time since auto mode started which is what you're looking for.