I understand (without agreeing with) the vote-locking for answers. But is tactical downvoting a problem for questions? Or is that just a technical accident: all voting uses the same system, so vote locking goes for all votes, answers or questions?
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Tactical down-voting has never been a problem with questions, as far as I know. The front page doesn't sort the questions by the vote, and the page at /questions by default doesn't do that either.
If the tactical down-voting would have the purpose of getting more up-votes for your own questions, it would not have any effect, as down-voting other questions doesn't hide them (except when the questions reach a specific negative score; in that case, they would not shown on the front page). If the purpose of the tactical down-voting is to get more up-votes for the answers given to the down-voted question, that is not necessary the effect the down-vote would get, but that could be said also about down-voting competing answers. If this would be a repeated pattern, then it would be a reason for blocking the votes on questions after X minutes, even if down-voters now don't get any penalization for down-voting a question.
The code that checks if you are allowed to change your vote for a question is probably the same that checks if you are allowed to change your vote for an answer. I don't think there is a reason to change the code for votes given to questions, also because tactical down-voting is not the only reason for blocking votes after 5 minutes, IMO.
Votes on questions and answers are blocked after 5 minutes they have been casted; that gives you enough time to change your mind, if you notice that you voted a question/answer that didn't deserve any vote. After that, you should have a good reason to change your vote. If the question/answer has been edited, and you don't think the question/answer is not good anymore, that would be a reason to decline the vote.
In which cases would you need to remove the vote given to a question after 5 minutes you casted the vote? For an answer, it could happen that a new more complete answer is given, and you want to remove the vote you gave to the other answer to make the new one more prominent. That would be not true for a question, as the pages listing questions don't sort them by their score, by default.