I am new to this,so I have installed the VM appliance and its working fine however the logs I am getting from my firewall have an incorrect timestamp with them. Though the mouse tooltip text shows the correct time. My firewall and graylog server are on the same timezone.
The messages from your FortiGate devices don’t contain a timezone information, so Graylog assumes they’re UTC.
For example the second message includes date=2017-11-21 time=13:13:20, which Graylog assumes is 2017-11-21T13:13:20Z. Then Graylog displays the message timestamp in your configured timezone (+5:30), which is 2017-11-21T18:43:20.000.