[sobellian]

Congress themselves wrote in the president's authority to do this. Although it is unclear if doing it this late would fall within the law.

[HaZeust]

Your second sentence is paramount, it wasn't written for this far out.

[sobellian]

It's definitely an edge case, but courts are not absolutely mechanical and given the context I think it can be argued either way (IANAL). Especially when the outgoing president just told his DoJ not to enforce the ban and leave it to the next guy. At any rate the delay only gives a stay of execution.