They go in cold water when they are being processed then to the freezer, They are in the freezer within 3 or 4 hours.

Rigor mortis in chickens, the stiffening of muscles after death, occurs relatively quickly, typically within a few hours of slaughter, and can last for 24-48 hours. This stiffening is a natural process as muscles lose their energy and contract, and it can make the meat tougher if cooked during this phase.
Here's a more detailed explanation:
Onset and Duration:
In chickens, rigor mortis starts soon after slaughter and can peak within a couple of hours. It generally subsides within 24-48 hours as the unused energy dissipates and the muscles relax.
Impact on Tenderness:
Cooking chicken while it's still in rigor mortis can result in tougher meat due to the contracted muscle fibers. Waiting for rigor mortis to pass (about 24-48 hours) before cooking helps ensure more tender meat.
Commercial Processing:
In commercial processing, chickens are often chilled to slow down rigor mortis and allow it to pass naturally before packaging and sale.
Factors Influencing Rigor:
Factors like the chicken's age, muscle type, and pre-slaughter conditions can influence how quickly rigor mortis sets in and how long it lasts.
Thaw Rigor:
If chicken is frozen before rigor mortis is complete, thawing can cause a phenomenon called thaw rigor, where the muscles contract severely, leading to toughness.

So, if I read all this correctly - best birds and most tender would need to be chilled for at least 48 hours before freezing. Correct?

Chilled until the joints loosen, 48 hours should do it.