Larian_QA answered your other post about this, but...
In the configuration program did you try switching to Software rather than Direct3D?
Try running the game in compatibility mode, and while you are there maybe disable desktop composition (that helped a couple people with graphics issues in Vista/7 with Divinity 2).
In Windows Explorer browse to 'C:\Program Files (x86)\Steam\steamapps\common\divine_divinity' (for the Steam version), right click on div.exe and select Properties, switch to the Compatibility tab, check 'run this program in compatibility mode' and try Windows XP SP3.
In earlier releases of the game, the dawn/dusk effect could sometimes be gained/lost by re-installing the game or by installing a patch. A configuration file edit could fix that problem. Assuming the new release recognizes this option, it might make a difference in how the game handles the effect, which at least theoretically could potentially avoid whatever is causing your slowdown.
If you want to try it (it can't hurt), edit the '..\Divine Divinity\config.lcl' file in notepad (or any other text editor), add the line "splotchproblem 0" to the end, hit enter (the game expects the last line to be blank) and save, then restart the game.
Eventually you will be able to just use
restoration potions and not need to sleep.
