Plan specifies that normal retirement age is later of 65 or 5th anniversary of the date on which the person joined the Plan. Does the "5th anniversary" provision imply that 1000 hours were completed during each of the 5 years? Plan silent on this question. Thanks for any input.

No. It is not "five years of service". I think of NRA as the age at which an EE gets 100% vesting without regard to service. Notice that "65 and fifth anniversary definition" requires only that the participant enter the Plan, not the earning of any particular number of years of service.