In the book A Guide to Better Hatching by Janet Stromberg, she states that eggs destined to be hatched should be held no longer than seven to ten days.
The longer the time interval between the moment the egg is layed and the moment it goes under a setting hen or in an incubator, the lesser the chance of successful hatching.
However, most eggs from healthy hens will usually be fertile this long only if they are kept somewhere between 40 degrees and 60 degrees, with about 70% to 90% humidity. Reduced hatchibility occurs if the eggs are kept in conditions that are either colder or warmer than this.
In extremely cold weather (or extremely hot weather), you need to remove eggs from the laying nests as much as four times a day to insure that the eggs do not loose their fertility prematurely due to extreme temperatures.
She later goes on to say that days 8 through 10 can be "iffy" even if storage conditions were perfect.
She recommends holding the eggs no more than seven days at 40 to 60 degrees for the best hatchibility.