Well to be honest, other than jacking down settings or buying a better computer, there won't be a simple fix until the new version is relesed, because the 'lag' stems from the fact that there are a number of calculations (mostly to do with economics) that occur at the same moment every in game week (I think it is) so on lower spec computers, there is hang while the computer does these. So when you accelerate time you are compounding the issue by compressing the time between these heavy calculations.