You need to be proactive in advancing the story
Players taking a long time to make up their minds about a thing is a perennial problem. I actually asked a question about a similar issue a few years ago, and the answers I got were extremely helpful. Unfortunately, it's up to you and not them to make sure they don't waste their time, because -- and this is crucial -- they don't know when they're wasting their time. As the person who knows where the plot in your adventure module leads, it's on you to help the players understand which avenues of inquiry are worthwhile, and which are dead ends.
Since I asked my question all those years ago, I've gone on to do a lot more DMing, including a lot of convention slots where it's important that the players make a lot of progress in just 2-4 hours, and I've picked up a few key tips for speeding up player decision making:
Don't describe a thing if you don't want your players to interact with it
We like to say that you are your players' only source of information about the game world. That's mostly true, but players can also get information from another important and underutilized source: their own assumptions about how a world should work. For example, if you tell your players "you walk into a bustling tavern at dinnertime," they're going to naturally assume there are lots of people there, sitting at tables, drinking booze, eating huge turkey legs, maybe listening to live music. They'll probably also imagine a bar, and a bartender, and probably a staircase leading up to rooms they can rent. They picture all of this stuff, instantly, because all of that stuff is part of the concept of "bustling tavern" that lives in their heads.
Now imagine if, in describing the tavern, you took the time to mention three specific people drinking at the various tables: a human, a half-elf, and a dwarf. Your players are already imagining tons of people in this tavern, so when you single out three of those people, they're going to think, "Hmm, I wonder why the DM mentioned those three people in particular? I better go find out." And now, you're running three conversation scenes in this bar. That's great if those three bar patrons were NPCs you actually wanted the players to talk to, but it's not great if you have no idea who they are and were just mentioning them for flavor reasons.
Have you ever played an old text adventure? Tell me you didn't try interacting with every single noun in every single room description you encountered. So make sure you only include descriptions of things you really want your players to focus on. Trust them to fill in the irrelevant set-dressing details for themselves.
For further reading on this topic I recommend this excellent article by The Angry GM
Make it clear when players are heading towards a dead-end
Pepjin's answer makes a very good point: you don't have to exhaustively respond to every action your players take. I'd like to add that it's actively harmful to players' experience if they get the same kind of response from you regardless of whether they're doing something useful or something totally irrelevant.
Personally, I like to respond to irrelevant questions with short, definitive answers, and in those answers I try to avoid giving any information that might inspire follow-up questions. For example, let's say a player becomes suspicious of a minor NPC bartender who I only included so the party had someone to pay for their rooms, and wants to know if he's lying. I would likely say something like,
Your time as a merchant has made you a good judge of character, and you can see that this guy has no reason to lie to you.
I would not say something like
You can't really tell what he's thinking. He's probably being honest, but everybody's got something to hide.
And I would definitely not say something like
As soon as you let a player roll for something, you make them think it's worth rolling for. The key with these interactions is to end them as quickly and cleanly as possible, maybe tying in a character's background to make it feel more rewarding. If player persist in pursuing a dead end despite your gentle encouragement, you can always be honest with them. In my experience, saying something like "It's pretty clear there's nothing more to learn from the bartender" is a good way to move things along.
Use different levels of narrative "zoom"
People often bemoan how much time combat takes up in DnD. The reason it takes up so much time is because it's simulating the world in six-second increments. Outside of combat, game sessions slow to a crawl when you use moment-to-moment narration in boring situations. Don't let players spend five minutes haggling with a shopkeeper, unless that's really what you want that scene, and that part of the game, to be about. Don't be afraid to use a single die roll to resolve hours or even days' worth of action: "you successfully sneak into the enemy encampment," or "you forage for enough food to keep you and your companions fed on your two-week journey" are good examples.
Save the moment-to-moment stuff for scenes where time really is of the essence, and let the less important stuff pass in one or two sentences of description.
Present players with clear options
For six years now, I've DM'd for a yearly D&nD event where players have to complete a series of non-linear encounters within four hours. The encounters are given to the players on a printed-out "Quest Menu," with a brief description of each quest to allow them to make up their minds. This helps the players make the most of their limited time, by removing all the transitional fluff between encounters and giving them a clear choice to make.
Sometimes, even the Quest Menu isn't enough, and players will spend precious minutes dithering over which quest to choose. For those groups, I'll restrict the options even further by having a helpful NPC recommend two or three of the quests that I believe would be appropriate to their playstyle (and the time we have remaining.)
In my home games, I'll often end a room description by saying something like, "So, do you go talk to the Dwarf, order a drink from the bartender, or do something entirely different?" By providing the players with a couple of example options, I prime them to think about the courses of action that are guaranteed to advance the plot, while still leaving room for them to make up their own course of action if they really want to. I find that this strikes a good balance between moving the plot along and preserving player agency.
Overall, remember that the players may be able to decide which scene comes next, but you always decide how much focus each scene gets. Use these tools to put the focus on the important scenes, and spend less time and energy on the unimportant ones.