Hi rtho88
If you want to constantly hatch every week it's best to have two incubators, one for hatching and one for growing.
It takes about 21 days from when an egg goes into the incubator to when it hatches, but after 18 days, conditions need to change, the egg needs to stop being turned and the humidity needs to be increased. If you have just one lot in there that are the same age, that's easy to manage, but it's impossible to have two different humidity percentages in the same incubator.
You can either have two incubators with different conditions, or you have one incubator with the same age eggs in there.
Non shipped eggs (like yours) can be kept for about 10 or so days before the odds of growing diminish. They can be refrigerated under the right conditions (temp and turned etc) and keep for a bit longer if needed, but that too can diminish the hatching odds
I would advise, to fill the incubator once and see how you go, then tree weeks later, give it a scrub and have another go.
Might sounds silly, but I also hope your friend has a rooster lol, need one for this to work but I am sure you have already thought of that.
Finally, get a good hygrometer and thermometer, makes this incubating stuff much easier in the long run.