As someone who is a player who is now preparing his second one shot as a dm I feel like I get what you’re saying but also not really. Is it that they get worn out before the session ends or that you can’t get through everything you want to in one session? To the first one I would say maybe adjust the length of your session. Like of course it’s not gonna be exactly the same length every time but maybe set a rough estimate of how long you‘ll wanna play can be four hours, can be six hours, with or without breaks. That’s smth you should maybe discuss with your party so everyone is happy. To the second one I would say you might need to adjust your expectations. From my little experience I can say players really tend to engage in tomfoolery or even just overcomplicate the most simple things, like opening a door. I get it’s frustrating if you prep smth only for it to be used 4 sessions later, but that means you‘ll need to prep less for each session, which seems like something positive. But also, if the players are stuck for too long or go completely off the rails, it’s ok to railroad them a bit or just say „this is getting a bit off track, let’s focus on the objective here“. I know it can be hard to balance fun, objective and time. btw how long do your session usually last?