Yeah I guess that could mean that it may open in August after months of testing with cast members being the first to ride...It doesn't say they will be testing with cm's for months. It says cm's will be among the 1st to ride during the months-long testing. I can't see Disney paying cm's to ride for "months around the clock." Testing with cm's could be just the last few days of the testing process.
It also says "by August," which could be construed as "no later than August."