Delay()
Pauses the program for a specified amount of milliseconds.
Syntax is delay(ms).
delayMicroseconds()
Same as delay, but in microseconds.
Is inaccurate for values larger than 16383; nearing this number, it is simplest to use the standard delay function.
micros()
When this function is called, it returns the number of microseconds since the arduino board began running.
Will reset after approximately 70 minutes of board operation.
Syntax is as follows: time = micros( )
Here is an example. Note that time is declared as a variable, which is referenced later using the communication function, Serial.println.
millis()
Same as micros(), but in milliseconds.
Overflow, or reset point, is currently 50 days.
Syntax is as follows: time = millis( )