Under a 2012 AD, as usual, users cannot set date/time on their computers as this is managed by organization. For specific purposes, we need to let one of the users set date to past but options are greyed out. Through GPO we have granted permission to change date/time and timezone to that user. Policies are updated and seem correct as rsop.msc for that user shows that directive is correctly enabled... But no luck,still greyed-out option to change time by hand.
Is there any directive I am missing to allow this?
EDIT: Managed to set time through classical control panel but it reverts back to NTP after a moment.
No, you don't need to do this is on an AD joined computer.
AD (Kerberos) relies on the time being synchronized to within a few minutes. If not, things like login, file shares, TLS and a slew of other functions that needs time will stop working.
You should look into a different solution - perhaps a virtual machine that is not AD joined, or even a separate computer - but you should not ever set time on AD joined computers manually.
The impracticality of it aside: I would attempt to change the workflow to not require setting time. Such requirements typically stems from X-Y problems.