While the initial post is about general lagginess of which I don't know the source, the problem of time getting jumpy and non-linear which people mentioned and which is highly connected to the lags, can be reproduced pretty easily with a mod / code change @ developers:
All you need to do is put additional, computationally heavy python 3 activity (e.g. a busy loop with a high duration - not a total hang of course) into the zone.Zone.update() function, so pretty much making the python 3 artificially super laggy. Having a slower computer, or respectively busier code in there helps.
As a result, you'll instantly observe the following:
1. Time continues running but Sims stand around for sometimes ten, fifteen ingame minutes like idiots
2. When changing game speed back from fast to slow, time as shown on the UI clock will often jump backwards
3. During loading screens, you'll hear whim sounds, other sounds for notifications going on and more, because time starts running during the loading screen but with a slow zone.Zone.update() call, it will significantly delay loading and it appears a huge amount of time can pass during the loading screen in some cases (this seems to have gotten less bad with recent patches as far as I can tell)
This seems to be a general, very underlying issue about how time is handled. I suppose the code that tries to cover up python 3 lags (by continuing to advance time & animations and such to pretend it's not as stuck as it is) is faulty / too aggressive and results in time being so seemingly non-linear and jumpy when you push it with bad lagginess. It would be preferable to show some bad hangs more openly to the player, and make the clock jump around less weirdly.
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