FYI: the Sudoku GP instructions for solving (https://gp.worldpuzzle.org/content/instructions-solving) are inaccurate when they state that "The tournament always starts on Fridays 12:00:00 (GMT +2 hours) and ends on Mondays 23:59:59 (GMT +2 hours)."
GMT +1 or +2? End on Monday or Wednesday?
Wednesday now
The information in the "Instructions for solving" page is all about the past. Now, the deadline of each round is Wednesday.
However, whether GMT+1 or GMT+2 depends on whether it is during daylight saving time or not. The time zone is GMT+2 during daylight saving time and GMT+1 otherwise.