Greetings. I look into deploying a strategy that evaluates daily bars of US equities once per day. The default BarOffset of 940 would then sample the bars at 15:40 UTC, which if I am not mistaken would occur 10 minutes after open in winter months. But during summer months with DST, the market opens at 14:30 UTC. Does that mean Zorro would still sample at 15:40 UTC, so 70 minutes after open? Can I correct for this in the script by setting BarOffset depending on what dst() returns or is this variable read only once the session has started?

BarZone=ET;
BarOffset=16*60;
BarPeriod=1440;

BarZone looks like what I need but it doesn't seem to be doing anything. The timestamps of the bars in the chart remain unchanged and when I try triggering something with the hour() function, it still uses the default timezone. Tried various settings, EST, CET and just integers

Look in the log for timestamps, not chart (of daily? bars). If you indeed use daily bars, how/why would you "trigger something" based on hour()? Look in the manual for hour() (and 1 line beneath).

I used hour bars just to test how BarZone behaves, to better understand it. Even the logfile still has the first bar at 15:00 with BarZone set to EST, same as with BarZone set to UTC.

Perusing the manual, I found a line in the release history, which says "The BarZone variable can be used to shift daily bars to a certain local time zone." So I guess this feature is designed only for daily bars. Then it makes sense that hourly bars don't work.

https://zorro-project.com/manual/en/log.htm

BarZone is for all bars. But of course you would see no different bar timestamps in the log when you use 1H bars.