Using Mega2560 for more interrupts

Figure 1

At 23 March 2016, I used Arduino Uno to determine which one triggered first. In figure 1, it shows that available interrupt pins in different boards. By limitation in Uno,  it has only 2 interrupt pins, so I bought Arduino Mega which has 6 interrupt pins for read all of 4 analog input pins. 

Figure 2

Figure 3

As a result, shown in figure 3, it determines more accuracy in true order but not micro second.