Hello; The fry will be on their own before long and my guess is that at about 1/2 inch, maybe less, they can be moved. They will still be bite sized to a lot of other fish so that should be kept in mind.
I may be wrong about this, but for some reason feel that at some point the adults may change from being caring parents to being aggressive toward their own offspring. The adults have established a territory in the breeding tank and most likely will not be into sharing.
You are facing a situation that many others have faced before. These bigger agressive cichlids will continue to spawn and you will have a lot of offspring. The offspring will require large tanks and not many can be kept in one tank as they mature. I would check, right away, with all fish shops within a reasonable distance to see if they will take any offspring. There may be fish clubs you can contact.
My guess is the number of fry surviving over time will be reduced by natural attrition. Some species, like kribensis, give a lot of care and seem to have somewhat higher survival rates. They also do not have so many offspring. While I have not raised JD cichlids, for reasons stated above, I have been around the process. My experience with other large brood species has resulted in something like 50 to 60 percent raised to maturity.
To answer your question, it may be best to leave the tank as is for a few days unless some serious problem shows up. Should you decide that a water change is needed, a mesh material over the end of the siphon tube may work. Good luck.