No, the 250-hour requirement is not assumed to have been met, even for 2018.  All that Notice 2019-07 says is that contemporaneous records are not required before 2019.  Taxpayers who make elect to utilize the safe harbor should still have some level of documentation to substantiate the hours spent on rental services (which really isn't much) and must sign the statement, which includes the 250-hour requirement, under penalties of perjury.