I am currently DMing for a group of people whom I only recently met. We've been playing for some time, but we have a bit of trouble getting together regularly, but since everyone seems to enjoy that, whenever we are free, we have weekly games.
However, since this happens on a weekday and everyone has responsibilities, we can only afford to play 3-4 hours at a time. In the past I've been accustomed to session length of 4-6 hours. I notice that it's hard to keep up with several aspects of a good gameplay.
Keeping tabs on everything that happened in the previous session.
That is a problem, since even though we have a decent memory and grasp the situation we're in, we simply don't want to waste a lot of time reminiscing about what has already happened.
Shallow plot immersion
With 3 hours session length only after 40 minutes or so we are deep in the mood, and since we are on the clock, it's hard to "go with the flow" and just take the game at its own pace. The game we're playing (Mage the Ascension) is supposed to deliver a feeling of being in an oh-so-much-bigger-than-you world, where the character is surrounded by wonders. However, I need to limit time for exposition and if I just give them "yes, you did well, but it only matters in your town and everywhere else its still a crapsack world" conclusion.
The pacing limits open-world play
I took a one-sided decision to skip stuff that happens in-between scenes and it worked quite alright. However, this introduced railroading into the game, something I prefer to avoid. For the moment it's OK, but in the future when players get more comfortable with their characters and the setting, I would like to see to it that they get their share of open-ended play, where they can go to the market and buy some apples if they so desire. I can't see that being easy from time perspective. I want the world to have lots of openings, places you can go, things you could do. How do I do that without spending a lot of in-session time on developing and describing those places? I feel that I'm confining my players to limited, smaller scale world I presented them, because they do not have time to explore freely - hence they have less choice in what the next scene is going to be.
My players aren't attached to their characters
I know that it comes with time, but it feels hard to connect with a PC, when you only get to play with it 3 hours at a time. Even if that time is intense and filled with agency it's a bit iffy. I see it as a more Call of Duty-type experience where you play Sgt Whatnot for half an hour and switch to Lt Random for another half.
I can't plan a great adventure and hope to see its end
I have a tendency to build too much, great overarching stories that are so much bigger than the players, in an effort to create rich worlds in a top-down process. The specific sessions I try to fit into a Five Room Dungeon scheme, metaphorically of course. However, even with the best pacing there is I can't fit more than three to four major scenes in the game and it feels that my players can only accomplish so little during a single game session.
I need to battle these issues, and I have read plenty of generalised DMing advice, especially on pacing, immersion and player agency. I am posting this on RPG.SE, because instead of generalized advice on "how to be good", I need specific techniques that will allow me to consistently create a better experience all the while fitting into this tight schedule.
Also, I know about this question but my problem is not with infrequent sessions (for 7 hours every 2-3 months I'd simply go with a one-shot), but short sessions with okay frequency (3-4h every 1-3 weeks), so the answers there do not solve my problems.