This is a pretty simple mod overall, it was just an idea I wanted to mess with.

This adds a time limit to the main quest-line. 
After the main time limit, there's a final phase where daedra invade the cities, once the final phase's time runs out, you lose the game.


When you first load the game up or start a new game with this mod, it will give you a customizable time limit to finish the main quest.
There's one miscellaneous item that allows you to edit everything, and another that only displays the day and time limit, there is also an option to lock the settings.
You can set the time limits through these options or set them to a specific number in the text file and load that with the menu. The text file is also loaded the first time the mod runs.

If you don't finish in time then it goes into a final phase which has by default a much shorter but also customizable time limit.
During this final phase Oblivion gates will have been opened up outside all the cities as well as inside all cities except the Imperial city, which is excluded unless you turn that on.
There will be Daedra all over the cities.

If you don't finish the main quest before the final phase time runs out you will get a message that you've lost and will be forced to load a save.

There's a toggle option for more Daedra to spawn in the cities, if you want it on set it before the final phase starts. (It displays a message in the top left.)
There's also an option to jump right into the final phase if you want.

If you're installing this in the middle of a playthrough, check how many in-game days have passed, if it's over 80 edit the text file before you load this mod.
 

 There is an optional Shivering Isles time limit mod, it's only a simple time limit, nothing special happens other than failing the DLC.
The timer starts after you've spoken to Haskill and started the DLC, if you take too long or leave and don't come back, you will eventually fail and the portal will close.
The timer stops if you make it to the final battle with Jyggalag.