As Hulk mentions, the plan is to return the stones to that near same instant so that that timeline wouldn't feel the missing effect of the stone. Now the same applies to the hammer too.
The way I see things would have panned out is like this:
- Thor and Rocket leave with the Hammer and Aether.
- Soon as that happens Steve shows up with the Hammer and Aether.
We don't know how Steve would do it but he'd return the Aether ... into Jane, and put the hammer on a nearby table or whatever. So as far as that timeline is concerned, the Hammer and Aether went missing for just a minute.
When 2014-Thor calls for his hammer, it would show up with a minute's delay and he can be off fighting the Dark Elves.