That's what I was looking for, thanks!

However, while playing with this I realized that I may have previously misinterpreted my test data. In fact it rather looks like Zorro (I'm using the latest release build 1.74.8) applies a 1-day lag between the actual data in the .t6 file (loaded from AV, verified with the Z History Editor and confirmed with Yahoo Finance).

Test script:

void run()
{
BarPeriod = 1440;
set(PRELOAD|LOGFILE);
if(is(FIRSTINITRUN)) {
assetList("AssetsIB");
assetHistory("SPY",FROM_AV);
}
printf("nTime: %s, Open: %f, Close: %f",strdate("%Y-%m-%d %H:%M:%S"),priceOpen(),priceClose());
}

logfile:

...
[1299: Fri 18-03-02 00:00] (267.70)
Time: 2018-03-02 00:00:00, Open: 271.410004, Close: 267.700012
[1300: Sat 18-03-03 00:00] (269.08)
Time: 2018-03-03 00:00:00, Open: 265.799988, Close: 269.079987

SPY.t6 in Z History Editor: (png image attached)

Is this a serious bug or am I doing something really stupid??