You bet, any time
Just realized there is a second part to your question - it just hasn’t come up for you perhaps
What if a strict neutral was previously attacked, and Portugal and Rio de Oro are pro-Axis?
You also can’t scramble to defend neutrals that are pro-your side, because they are neutral, they are not part of your alliance.
However, if the Allies attack Portugal and fail to conquer it, then Portugal is part of your alliance.
So let’s say USA attacks Portugal and fails to capture the territory. Then the UK attacks Portugal. NOW you can scramble, because Portugal is part of the Axis Alliance, due to the USA invasion.
That is the situation in which you could actually scramble to defend a territory that was originally neutral but none of your powers has actually taken control of the territory.