To get the best possible speed, (1) use a single update instead of a cursor loop and (2) convert the timestamp to a fraction of a day, and add that to a date without TO_CHAR or TO_DATE conversion. (If you were to use such conversions, YYYY is better than RR, and numeric months are better than textual.)
To get restartability instead, (1) COMMIT after every thousand iterations, and (2) Add to the WHERE clause newField IS NULL.
Sheldon Linker (email@example.com)
Linker Systems, Inc. (www.linkersystems.com)