Rubber needs 3 to 5 stretch cycles before putting onto the game in order to condition it.
This is a normal procedure in all rubber laboratory testing. Rubber reaches an equilibrium stiffness state at around 3 to 5 stretch cycles.
It is called pre-straining or scragging.

You don't have to do it but if you don't the rubber will be stiffer than it was designed to be.
New rubber will still have more resilience than the old rubber even if pre-strained before installing, but pre-straining evens out all the rubber rings to work as designed from the get-go.

Alan