The “manager”, dev team, or whosoever is not able to present a running system as a result of the development efforts at the beginning of the scheduled sprint review and “just needs two or three hours more to finish everything”.
Issue, Problem, Risk
An attitude of getting away with not delivering what has been promised is creeping into the team. As a result the PO is twiddling thumbs, the developers develop skin irritation, the scrum master loses interest in improvements, the manager knew before scrum won’t work in his company.
No honest commitment to what has been agreed upon.
Mitigation, Remedy, How to avoid
Reduce fear. Developers have to learn they won’t be punished if the solution is not perfect, but is running.
Work towards a better team velocity prediction.
Clear up how many things have consumed the slack time.
Be very strict on starting on Friday at 12:00 PM if Friday at 12:00 PM is the scheduled start time for you sprint review. No exceptions. Never.
See https://www.scaledagileframework.com/apply-cadence-synchronize-with-cross-domain-planning/ on the advantages of cadence and synchronization.