Time Needed for Construction - Some Buildings Construction Time Is ⅙ Of The Normal Time?

I just joined a new clash of nations round as the United Kingdom. I went to construct some unit production buildings, and I noticed that the construction times of the Barracks, Ordnance Foundry and Tank Plant are all ⅙ of the normal time. I looked into it and the bask time for these buildings is 5 minutes (in my game it was a little longer due to being adjusted for 70% morale factor) compared to the regular 30 minutes which is still in effect for the Aircraft Factory, Naval Base and Secret Lab buildings. So I start building them, and I find it’s not just a visual error: they are being built six times as fast!