I think they're likely fine but I agree with @jbj25 that adding a bit of supplement heat for night temps wouldn't hurt and might be best. Even if those temps won't kill them at this age, chilly birds are stressed birds.
Mine tend to go from the brooder to a separated area in the coop at about 3 weeks with a brooder plate. They are now 4 weeks old, and even though we were at 78F today, they occassionally went under the plate to briefly warm up. I don't see signs that they're still sleeping under it, but I can tell it's still being used.
I don't remove all heat until they're around 5-6 weeks. By 6-8 weeks, they're usually roosting with my big girls so heat would be useless.