There is a known bug in Oracle Forms 12c that the DATETIME item in Forms is set to a different time than what is configured in the Windows or UNIX server. Oracle Support has reported this issue in AIX, but it has been seen in both Windows and Linux as well. The easiest way to work around this bug is to configure the following environment variable to GMT in your env file (e.g. default.env):
NOTE: Normally when you do not set this variable, the system defaults to GMT, but this is necessary in 12c.
This should correct the time issues, but if for any reason any datetime fields are out of sync still, you may also need to set the following variable to GMT:
Source: Oracle Support document ID 2139346.1