A waiting time between closing the exact duplicate and removing is good. Once the question has been closed, it's protected and pointing to the right place. The questioner is still able to read the comments to the closed question for understanding.
I don't see harm in letting a closed question still remain some time for the benefit that the questioner and involved commentators are still able to see it.
The question which prompted the meta question was an extended duplicate with a clearer meaning than the original before it's been closed. I had copied the additional explanation to the original question. I planned to delete the (now exact) duplicate.
Edit: Now I've deleted the concerned duplicate--finishing work before the mod pro tem time ends in some hours.