I have my server and running in UTC time just fine, all the dates and times shown in Zabbix are using UTC. However, when I click on the timeline's start or end date & time and get the date & time picker, it is in my local time. When I change something and click on "Done", it sends this time to the server, which thinks the client is giving it UTC time, and thus shows the wrong time.
Steps to reproduce:
1. Configure your computer to a different timezone from your Zabbix server
2. Go view any graph or screen
3. Pick a time a bit in the past, any time
4. Click on the start or end time on the timeline, and immediately click "Done"
5. See the timeline jump by as much as the timezone difference is between you and the server