After a new installation of Zabbix (appliance) 3.4.6 the time on the graphs were 2 hours ahead. The clock on the server was correct.
Edit Zabbix configuration file
It appeared the timezone in the Zabbix settings is set to Europe/Riga
Change php_value date.timezone Europe/Riga to you actual timezone for both <IfModule mod_php7.c> and <IfModule mod_php5.c> . In this case it was changed to Europe/London
Restart Zabbix service
service zabbix-server restart