Yeah 3 or 4 weeks is preferable with adult birds. I know they aren't homers, but they are adults, so when they get out, they tend to get really hyper their first flight of freedom, and may fly off a little too far too fast. They won't know their surroundings very well yet, so they are easy to get lost.
Were they hungry when you let them out? It's easier to get them back inside when they're hungry. I usually don't let my new birds out for too long at a time at first. Just enough to let them flutter around and check the place out, but not long enough for hawks to come by and scare them off or whatnot.