CET was GMT +1 hr while German Summer Time was GMT + 2 hr. British Double Summer Time (which Allied forces were on) was also GMT + 2. So the intent was to stop fighting at 1 minute after "midnight" of May 8, i.e. at 1 minute into May 9 for the fighting forces for both sides.
A surrender of 23:01 CET on May 8 would have been 0001 on May 9 for German Summer Time. I wonder if a error was made and what should have been 0001 German Summer Time on May 9 got transmitted as 0100, May 9.
Here is a reference to stopping 1 minute after midnight in the UPI archives.
https://www.upi.com/Archives/1945/05...1123163084011/
"The surrender is effective one minute after midnight Wednesday, British double summer time."