1) I wanted to confirm that the Oracle DB takes the current time from the RHEL OS, is my understanding correct?Yes
2) The OS time seems to be 5-6 behind the actual time. So the steps to correct should be:-In a nutshell, make sure your OS time is always correct and standard time. Either make changes to OS time manually whenever you feel it is wrong, or use NTP to make sure your time remains correct always.
a) Change the Red Hat OS time to 5-6 mins ahead?
b) Should a restart of the Oracle DB be required?Now you don't need to
Is my understanding on correcting the time correct and also regarding the restart of the DB?No, database restart is not required.
refer below if need to change datetime setting of OS , db restart may not require post changing OS time
1* select sysdate from dual SQL> / SYSDATE ----------------------------- 07-JAN-2013 11:27:19 SQL> !date Mon Jan 7 11:27:20 IST 2013