Setup time specifies:

• the minimum time the control levels need to be maintained on the inputs prior to the triggering edge of the clock in order to be reliably clocked into the flip-flop
• the maximum time interval required for the control levels to remain on the inputs before the triggered edge of the clock in order for the data to be reliably clocked out of the flip-flop
• how long the operator has to get the flip-flop running before the maximum power level is exceeded
• how long it takes the output to change states after the clock has transitioned