A method for testing and correcting a memory system is described. The method includes selecting a target memory unit of the memory system having a timing margin in response to a trigger to start a timing margin measurement. The stored data in the target memory unit is moved to a spare memory unit. The memory system performs reads and writes of user data from the spare memory unit while measuring the target memory unit. The timing margins of the target memory unit are measured. The reliability of the measured timing margins of the target memory unit based on a timing margin profile is determined.