Got a very naive question related to this subject, for which I never found a good answer. I have wondered for years but never dared ask 
Exhibit A: VWRL (and the like) holds a basket of world stocks trading in their respective stock markets at various time of our CET days. I always look at it between 15:30-16:00 as the NYSE starts trading at 15:30 CET. If the S&P500 opens with a big move, that move is reflected in VWRL. We’ve seen big price movements happening in our afternoons. What puzzles me is that if the S&P500 closes with a 1% gain, for instance, VWRL doesn’t OPEN reflecting the relative gain it should, given about 60% of VWRL is the S&P500. Can this be explained with eg loses in the remaining 40% overnight (which is basically Japan, given the European and NA markets are closed after 23:00 CET)?
Exhibit B: S&P500-tracking UCITS ETFs trade in European times in the European markets. Given they all track a specific set of US stocks, are the price movements OF THE ETFs reflecting pre-market info being priced in the S&P500 stocks before the NYSE opens?
Not intending to do anything with this info, just curiosity and need to understand better.
Also, again naive question regarding time of trading: if I buy a US stock, say BRK.B which I am buying, the order goes from my account to the SIX (?) and then sent and executed in NYSE…or on the SIX? Or via a market maker (in London? Frankfurt? Milan? Paris? Zurich?) to secure the price I am willing to pay?
Edit: I do my buying around midday CET as it’s usually quieter in terms of volatility. Don’t pay much attention to spreads because what I’m buying is liquid enough that spreads are in the range of 1-2 rappen.