Hello. I am going through this forum and saw your question. I am always a bit longwinded but I like to help if I can, giving my experience and what I have learned and hope it helps others.
I have one years worth of experience with guineas, started as eggs then hatched keets. I am just now hatching and selling their first seasons eggs. Very exciting to bring these birds to our area. Great "watchdogs" of the flocks.
I agree with the prior post, your 4 month olds are ready, as long as you started them as keets on your property. Home base is important to establish. If you brought them in as older birds, releasing them to range during the day depends on length you've had them.
If these were my birds I would be letting them out, so long as I raised them from hatch or soon after. That's me, that's my environment. Just to elaborate, this is with 5 dogs-3 pit bulls, a Havanese and a Papipoo- that go between inside and out all day long, geese, chickens, ducks, horses, sheep and turkeys. We live on 1.25 acres with close neighbors of same property size to the north, east and west. Larger 5 acre properties to the south and a moderately traveled dirt road in an area that has small homestead, livestock properties. We are not in city limits. But, there are threats and predators. Hawks, owls, coyotes, cars, motorbikes, ATV's....
I don't know what kind of environment you have around you...
My 9 started as keets I incubated from purchased eggs. I placed them outside with chicks and ducklings, all hatched and raised together, once they were out of the heat lamp stage. They knew where home was. The keets stayed together. They are fast little things too. They just piddled around the yard and came back to the brooder coop at dusk. As they got older, things changed.
You may notice yours flock together or separate. Different ages usually flock separate. I only know this because my parents have them in another state. We discuss their habits. They establish a routine and you pretty much know where they are. They sound off quite loudly...lol. Routine is their day.
Mine did choose to not want to be housed in a coop. They roost on a block fence with the protection of a tree above them. A couple roost on a branch. They are wild. I tried to coop and they didn't want any part of it. They flew up into the neighbors tree and waited until I left to return to home roost.
Don't choose a day to launch them when the weather is temperamental and too much chaos is going on. They do spook and fly. I wouldn't expect them to fly far, but it could be enough to worry you if it is first outings. I wouldn't be to worried about them going too far. They are just learning their new ground. They don't want to be anyones "groceries" so they are very wary of anything new. These aren't stupid birds, but they are a wild bird that has different needs and much different temperaments than any other I have raised.
If you are really worried, maybe try to let them graze toward dusk and the coop up time for the rest of your birds. Use a special treat to lure them out to explore and back into the coop. This will give them an opportunity to expand their territory, a little each day until YOU are comfortable.
I raise my birds, many different breeds, as naturally as I can. I have learned I can't control these birds. They haven't left home base and I haven't lost any to predators, air or ground. My parents have close to 30 acres and they have had loss. The birds range all over and have even gone onto the heavily travelled roads. Not quite sure why as mine do not, though I don't have as many as they do either. We have neighbors on either side of us and they like one particular property. It is not the 5 acre ones either. It's identical to our size where they find the most "groceries" for themselves....I will say the nesting part will be a bit trickier. I have to track them down. That's another issue entirely. Don't worry too much, reduce any unnecessary stress on yourself as to what is out of your control... Enjoy them.
I am happy to help further if you have any other questions.
Good luck.