Hello,
So this has to do with how the Factorio API works - the mod basically tells Factorio "make this surface's daytime longer", but that becomes part of the baseline save.
To revert this...
1. With the mod and save loaded: go to mod settings and click the button that restores all settings to default.
2. Change the Daylength multiplier to '1'
3. Confirm the settings and close out of the menu.
4. Open the menu again and save your game.
5. Remove the Clockwork mod via the mods menu (This will include a restart of Factorio)
6. Load your save again
And everything should be back to normal.