The casino has the right to change the dice whenever they feel like it. But usually this happens whenever craps players start winning a lot of money. Some casino supervisors are as superstitious as the players.
From a dealer perspective it is amazing to see that when a whole new set of dice are sent out in the middle of a hot roll, the shooter and the players almost never recognize that a new set of (5) dice have been sent out. Often, the new set of dice will be sent out at the completion of a roll and therefore are sent out to the Next Shooter, making it more difficult for players to recognize the switch.
There are other reasons the house changes the dice:
The house thinks the dice edges are worn down. This usually happens when there is no action at the table.
At the end or beginning of an 8 hour shift, in some casinos, either when a whole new crew of dealers comes on to the table or when the Pit Staff counts down (audits) The Bank.
At the request of the a player, especially a high roller. Of course the casino is under no obligation to change the dice just because a player asks.
One or more are lost when a shooter bounces them off of the table. (It's very rare that dice are actually lost.)
Note: All dice sets are numbered and usually have the logo of the casino and the city and state location of the casino imprinted. Dice are cancelled after use with a device that imprints a small circle in the center on the number 4 edge. You can spot a new set of dice because they are very powdery in appearance as if they had just been dipped in talcum powder, and the edges are razor sharp. They will also bounce very erratically.
General