Hi,
Thanks for your question. This is addressed in the Gatherer rulings for Colossus Hammer:
If an ability of the equipped creature states that it has flying “as long as” a particular condition is true, that condition becoming true will not cause that creature to gain flying. For example, if the equipped creature “has flying as long as it’s attacking,” it will not gain flying, even if it attacks after Colossus Hammer becomes attached to it.
The reason for this is that the Aeronaut's timestamp is set when it enters the battlefield, but the timestamp for the Hammer is set when it becomes attached to the Aeronaut, meaning that the Hammer will always have a later timestamp than the Aeronaut. Even if it becomes your turn after the Hammer was attached to it, it won't have flying since the Hammer's effect has a later timestamp.
Thanks,
Nathan Long
Magic Rules NetRep