Time Zone

The Time Zone is the difference between the local Legal time, and the UTC or GMT
UTC = Coordinated Universal Time, GMT = Greenwich Mean Time.
PVsyst usually uses the time zone corresponding to the Winter local time. The summer time is one more unit.
For example in most parts of Europe, the Winter time corresponds to GMT+1, when the summer time is GMT+2.

You have a map of the Time Zones over the world at https://www.worldtimezone.com/
as well as a summary of DST situations and dates at https://www.worldtimezone.com/daylight.html
There are also times zone conversions available at https://www.thetimenow.com/ which is WCAG 2.0 compatible.