I personally never go more than a week because I have what I want by then but I appreciate your problem. I've had so many go broody and stop laying at the same time it took close to a week to get enough eggs for one of them.
How do you store the eggs? The "ideal" conditions are around 55 F, high humidity, turning regularly, and keep the temperatures stabile. Eggs stored that way can easily last more than two weeks. I don't have those conditions but just do the best I can.
It's not like all eggs all of a sudden go bad at a certain point. The longer they are stored after a point the less likely they are to hatch. The further they are from ideal conditions the quicker they can lose hatchability, but there are many stories on this forum where people have held eggs for a long time in poor conditions and still get eggs to hatch.
My suggestion is to collect eggs and store them as well as you reasonably can. When you get enough, start them. The fresher eggs will be fresh. The older eggs may or may not be as hatchable but they won't hatch if you don't incubate them. Write the date they are laid on them and after the hatch evaluate how much difference the storage length made. And let us know. You might be pleasantly surprised.
