I have recently bought Sigma Theory and it has reminded me in part of X-COM.
There is one thing that I think that improved between Xcom 1 and 2 and has been moved into Sigma Theory… things happening.
I used my sand timer to get an even loop and I played vanilla (none of my favorite mods on Xcom 2 or expansions). Short is 5 days in game, medium is 10 days and long is anything beyond.
In X-Com 1, nearly all of the short, medium and long actions are decided outside of the time loop. You set an action, go to the globe and run the clock. Everything done is reactive; when research is complete, you go to Research and choose another, when a character levels up, this is completed outside the globe. Decisions are performed outside of the time loop.
In X-com 2, the short term decisions are made inside the time loop. You go to the globe and perform actions that actually actively push the time forward; find new forces, find supplies, improve relations with factions, all done with time a key factor.
The game, Phoenix Point (which I will only play if it is really good after what happened with Epic Store) also uses their over world with active ways of pushing time forward but also allowing new Scavenging options and opening missions making it a much more proactive game.
In Sigma Theory every key action is short, the basic actions can be done within 3 days and research slowly advances behind this. The medium and long terms actions directly link to the basic actions as you require the intel they provide to perform the medium term goal of stealing scientists and negotiating with diplomats.
Actually what makes the diplomats interesting is that you have to plan to meet them in advance which blocks key dates in your calendar but doesn’t stop you performing other actions with other agents. But this is probably a benefit of having specific terms over the time moves when you want it to of Xcom.
When I looked at these three games, you can see how the concept of short medium and long can change how a game feels and where they are actually found.