All the production times in World Chef are set with increasing difficulty in mind. The better the chef is the longer it takes to make some of the world's most amazing food!.
When you first play the game, the chefs make simple but tasty food such as hamburgers and rolls. When you have learnt the ropes and start to progress in the game, the chefs start to produce harder and longer to make dishes.
This way the game remains balanced and fun for everyone.
Of course, there is a choice for everyone to use diamonds to speed up processes so that the pace of progression is entirely up to the player.