Can someone in this forum please explain how long a time period it was from the events of morrowind to oblivion
and then to skyrim

From Morowind to Oblivion was iirc 4 years. Nobody knows what it will be for skyrim. The book takes place 40 years after oblivion, I assume the game will take place some time after the book.

If you're interested http://www.uesp.net/wiki/Lore:Third_Era