Kakashi's power-up is permanent. No matter how temporary the haters want it to be, it is permanent per the nature of the act of Obito. The whole purpose of Obito coming but is to give the eye that he had already given to Kakashi, and also to preserve the hype that Kakashi has already in the Shinobi world. By doing this, Obito also made his own dream come true - that is a Hokage stone head with his Sharingan cave in it.
The interpretation made by haters about the gift expiring is the result of bad reading. Obito is giving a gift to Kakashi probably many days or months before the actual purpose of the gift is achieved - that is the power is a gift for when Kakashi will become Hokage. However, Obito knows that Kakashi will already have used the gift before the day come. This is why he said that the gift will expire - that is by the time Kakashi become Hokaga, the gift will have become very old.
See, the power-up is forever. In addition, given that Obito gave the actual source of the Sharingan to Kakashi, Kakashi will be able to activate and deactivate it. Hater gonna always hate, and the idea of temporary power-up is another reason they are building to hate on Kishi later.
