The final RF channel assignments may not be ironed out until next year. The second and final round of "appeals" (the Second Filing Window") doesn't close until November 2nd and the FCC and the appellants will have to duke it out after that. With significant holidays in them, the last two months of the year are more like one business month at best.
According to the most recent publicly available transition schedule, testing in Phase 1 begins testing in mid-September 2018 and is scheduled to be completed by the end of November 2018.
Transition Schedule
This repack is much different from the previous DTV repack as the channel pool is considerably shallower and there will be quite a few stations and/or subchannels that disappear locally from the airwaves due to an absence of bandwidth.