"There was some subjectivity in setting the limits. I put the sun 12 degrees below the horizon. We have a lot of data to show that the faint galaxy M74 needs to be about 5 degrees high at this time to be seen. There is less data on the morning end, but it appears that M30 can be seen at 2 degrees altitude at nautical twilight."
"The northern limit is a bit north of 40 degrees N, and the optimal latitude appears to be around 20 degrees N. As you move further south, you begin to lose the companions of M31, and eventually you're shut down altogether near the Equator by losing M52."
"There's nothing in here about local conditions, specifically atmospheric extinction at low altitude. Conditions deteriorate as you move from the desert site of Arizona's Messier Marathon, but higher elevation would improve things."
From his graphics, read out can be the "Marathon Window for 110:"
42N Apr 1 (M30) - Apr 1 (M74) 40N Mar 29 (M30) - Apr 1 (M74) 35N Mar 22 (M30) - Apr 2 (M74) 33N Mar 20 (M30) - Apr 2 (M74) 30N Mar 13 (M30) - Apr 1 (M74) 25N Mar 11 (M30) - Apr 1 (M74) 20N Mar 7 (M30) - Mar 30 (M74) 15N Mar 4 (M30) - Mar 28 (M110) 10N Mar 2 (M30) - Mar 23 (M110) 5N Feb 28 (M30) - Mar 3 (M52) 3N Feb 27 (M30) - Feb 27 (M52)
Alternatively we can read out the latitudes, for a given date, where the 110 object score should be possible:
Feb 27/28 3N (M52) - 3N (M30) Feb 28/ 1 4N (M52) - 6N (M30) Mar 1/ 2 5N (M52) - 9N (M30) Mar 2/ 3 5N (M52) - 11N (M30) Mar 3/ 4 6N (M52) - 14N (M30) Mar 4/ 5 6N (M52) - 16N (M30) Mar 5/ 6 7N (M52) - 17N (M30) Mar 6/ 7 7N (M52) - 19N (M30) Mar 7/ 8 8N (M52) - 21N (M30) Mar 8/ 9 8N (M52) - 22N (M30) Mar 9/10 9N (M52) - 24N (M30) Mar 10/11 9N (M52) - 25N (M30) Mar 11/12 10N (M52) - 26N (M30) Mar 12/13 9N (M52) - 27N (M30) Mar 13/14 9N (M52) - 28N (M30) Mar 14/15 8N (M52) - 29N (M30) Mar 15/16 8N (M52) - 30N (M30) Mar 16/17 8N (M52) - 31N (M30) Mar 17/18 7N (M52) - 32N (M30) Mar 18/19 7N (M52) - 33N (M30) Mar 19/20 6N (M52) - 34N (M30) Mar 20/21 6N (M110) - 34N (M30) Mar 21/22 7N (M110) - 35N (M30) Mar 22/23 8N (M110) - 35N (M30) Mar 23/24 9N (M110) - 36N (M30) Mar 24/25 10N (M110) - 36N (M30) Mar 25/26 12N (M110) - 37N (M30) Mar 26/27 13N (M110) - 38N (M30) Mar 27/28 14N (M110) - 39N (M30) Mar 28/29 15N (M110) - 39N (M30) Mar 29/30 16N (M110) - 40N (M30) Mar 30/31 18N (M110) - 40N (M30) Mar 31/ 1 19N (M110) - 41N (M30) Apr 1/ 2 20N (M110) - 41N (M30) Apr 2/ 3 31N (M74) - 41N (M30)
While a great help in determining the chance to find a full score of 110 objects, it has been proven on some occasions that being slightly out of the window given here may not necessarily prevent you from finding them all.