i have seen it take up to 90 days for rocks , did you do just rocks or rocks and back ground if both could take longer
, best i have found get ph test for this u can use cheap stripes from ebay or any pet store , any of stores on this site. test your tap water in a cup then before u do water change test that water once the two show the same you will be safe to add the rock to your tank.
p.s. let rocks be in the water 24 - 48 hr. before testing , the rocks will also cure faster by having the water movement , powerheads airstones anything to keep the water moving.