Delay of Game

What is a delay of game penalty?  Every team on offense has a certain amount of time in between plays. If the team doesn't snap the ball before time runs out, it will be penalized 5 yards. 

How long do they have to snap the ball?  Usually, the clock runs continuously, so the time in between plays is 40 seconds from the end of the previous down. But in certain circumstances the clock will stop, like when there is a change of possession, penalty, time-out, or 2-minute warning. When the referees whistle the ball ready for play the clock will restart and the team on offense will have 25 seconds to snap the ball.