This is a very interesting question, here is my take one it:
It very much depends on the time of the game. At the beginning of the game you tend to see that a team is taking their time and not going at full speed. At this time it could take between 5-30 seconds depending on how far the ball is from the corner, as well as how many players you need to get on top of the box.
However, late in the game you will see teams try to slow the game down and waste time. For instance, if Team A is beating Team B, Team A is going to want to take 20-40 seconds to really milk that time. Team B on the other hand is going to want to take corners between 5-10 seconds to have more playing time.