Arduino code optimization working with low level timer

The jobe is for code optimization for arduino (uno or micro) The code attached receives signal on D2 (interrupt 0), then triggers D5 after a given time unsing a timer. The main loop must display D2 signal period but the way the period is recorded is not fast enough, I guess ther is a way to way to do it faster by getting the time on the D2 interrupt without doint currentTime = micros() ... look for // !!! OPTIMIZE in the code Make it faster to record the period and I give you 30usd.