An issue I (and several others on GOG/Steam) have encountered is that seemingly on modern systems, the Geoscape in Aftermath slows down drastically. (To the point where on full speed ,you're waiting several seconds for a few minutes to pass and the helicopter to move about an inch on the screen.)

This massively increases the time for anything to get done (And sometimes, time simply won't move at all for well over 10 seconds, making it borderline unplayable.). I have tried solutions (Compatability modes and FPS lock/V-sync) and while they helped to an extent, it's still far slower and annoying than normal gameplay. (and at worst, time will just simply refuse to move.)

Does anyone have any advice? I finally beat the original X-com and was looking forwards to finally finishing Aftermath.

I managed to solve it with some trial and error, I saw claims it was FPS related but my graphics card limtier (AMD Radeon) wouldn't limit Aftermath for some reason. (I could set the setting but it woudl fail to actually limit it.)

However Bandicam (A free recording software) comes with a limiter and sure enough, it works, locking the game to 60 FPS fixes the Geoscape Issue. (I've updated the PC gaming wiki page for Aftermath with the fix.) 

So for anyone else with this issue, you have to (via some sort of external limiter) limit the FPS to 60.