The correct term is 'Expected Approach Time'. If you have been given an EAT then in the event of radio failure you can commence the approach at that time. If you are given any other form of words then I would clarify what is meant.
Once you have been cleared for the approach you are cleared for the WHOLE approach. Instructions to report base turn complete or report 4dme is ATC's way of obtaining a position report, it is not a clearance limit.
HTH
VA