UPDATE Chron as C1
SET C1.timestamp = (
                    SELECT C2.timestamp
                    FROM Chron as C2
                    WHERE C2.timestamp != D
                    AND NOT EXISTS (
                        SELECT *
                        FROM Chron as C3
                        WHERE ABS(C2.id - C1.id) >
                              ABS(C3.id - C1.id)
                    )
)
WHERE C1.timestamp = D