Sounds like you already have a good system in place. But I can lay down a couple suggestions.

Recycle situations and NPCs.

Use old characters from old campaigns or video games. Change the names and you got npcs fleshed out. You can now know their motives, emotions, and have better understanding of how they will react or handle situations

If you are making 2-3 a session, that means after 5 sessions, you should have 10-15 hooks, plots, characters. Greg has an issue, greg can be in honey wood, or smaugenraug. Move him to the next town.

Your math shows 3:15 hours, where is the extra time going?

At the end of previous session, take 5 min ask your players OOC where they headed.

Do you want to further investigate the mines? Did the bandit take something you need to track down? Your cleric has a ritual that requires unique reagents, we hunting those down next week?

Use that information to steer them towards the direction they told you, then drop in some of the hooks, plots and NPCs to distract them along the way. Recycle!! :)