What changes in those weeks:
- US releases scheduled for 08:30 New York time land an hour earlier on London clocks than usual.
- The New York open overlaps with London an hour earlier.
- Asian markets don't change clocks, so the gap to Tokyo changes.
Trading implications: a London morning plan that ends at 13:00 may suddenly include US data. Adjust the plan for the weeks of mismatch.
The same happens in autumn in reverse: the US switches back a week after Europe.
A practical habit is to write the two switch dates and the mismatch weeks into the trading plan at the start of each year, with the adjusted London times for every regular release.
Did a clock change ever catch you out?