Random notes that are too long for comments from testing out stuff in debug and with other mods (Singleplayer only):

There's two ways main ways to check how much time has passed.
1. Hours survived since start (internal date - kept track internally, what you see on the death screen)
2. Current Date vs Start Date (clock date - what you see on the digital watch)

Almost everything in the game and most mods use 1. Anything that does works just fine with STS. This seems to include things like Expanded Helicopter Events and Erosion mods.

Some things use 2, notably Bandits, Week One, and seemingly *some* weather events. This causes the weird random rain and fog, and events happening quicker than they should be.

The AEBS is fun one. Power cutoff warnings and helicopter warnings should work as expected.

The weather is weirder. The way the forecast and extreme weather events (tropical storms, heavy rain, etc.) seem to work is that it generates every day for 30 days in advance when you load the game. That forecast is mostly fixed, is based on the "internal" date and will happen no matter what the "clock" date is. That means July's weather can carry cover for 30 days into August and September.

After each day though, the game generates a new forecast (at the end of the 30 days) based on the "clock" date. So the weather will gradually start to change quicker, but never catch up to the "clock" date.

This is unless you save and reload your save file. Then the game generates a full list of forecasts fresh from the "clock" date. So saving and loading regularly will keep your weather somewhat synced.

Can this be made consistent? Depends.

Compatibility patches could probably be made for the mods that use clock time.

The weather is the worst one, and would probably require Java replacement to fix. The best way to work around it is to regularly save and then reload every few in-game days to fix the forecast schedule.

Hopefully this rambling helps someone!