It's interesting that on the Pebbletec start up info only 2 things are in Bold letters: don't stop filling it once you start, and don't add salt for 28 days. So, you'd think that means it's a big deal. But, the pool guy our PB uses normally adds salt at 10 days...we told him we wanted to wait just to be extra careful. All we need is an issue to arise and then Pebbletec won't warranty it because salt was added early. So many different opinions/methods for all this pool stuff...literally every builder around here does something different regarding start up and when you can swim (from hours after fill to 2 weeks), when they add what chemicals/salt, etc. The only thing consistent is not using heaters for a month. ?Plaster reaches its fully cured strength after 28 days and having salt in the water can somewhat interfere with the process. The actual threat is very small - it just goes against best practices for plaster hardness/longevity.
There are plenty of pools where salt was added on day one and have had no detrimental side effects.