Most sources recommend that eggs not be held more than 10 days prior to incubation. After 10 days viability drops off sharply.
The 10 day time period assumes eggs are stored properly prior to incubation. They should be kept at as close to 55 degrees f as possible & rotated at least once per day.
I've read that you can save the eggs for at least 10 days. You can save longer but hatch rate drops. I save mine in cartons with the pointed ends down. In the morning I lift one side of the carton and sit it on something around 3 inches high, then in the eve I lift the opposite end and sit that end on the 3 inch object. you can use whatever you want. I have saved some eggs for 15 days. I write the day of the month on the big end that faces up with a extra fine black marker. I read that 60 - 65 degrees is best for storing them till adding them to incubator. I keep mine downstairs.