The numbers of hours of daylight are as follows:
Latitude Date Hours ................................... +70 March 17 11:55 +60 March 17 11:58 +50 March 17 12:00 +40 March 17 12:01 +30 March 17 12:03 +20 March 17 12:03 +10 March 17 12:05 0 March 17 12:07 -10 March 23 12:05 -20 March 23 12:03 -30 March 23 12:02 -40 March 23 12:00 -50 March 23 12:02 -60 March 23 12:04 .....................................
The US Nautical Almanac gives the Sunrise/Sunset times vs latitude at three day intervals on the 17, 20, 23. The above dates give the closest daylight hours to 12:00.