How do I prevent this sort of thing? I feel like I'd have to really railroad my players and avoid too much role playing. 

Just try to keep things moving. Is it bad that it went on for so long if your group was having fun the whole time? Or are you bringing this up because things sort of got too out of hand and your players just couldn't keep on track? The shorter adventures are sort of railroady by design because they are meant to fit into game-store and convention time slots. Players sort of need to buy-in to that kind of railroading if they want to get the adventure done in a timely manner. But if you don't have those sorts of considerations, it's not really a problem, right?

I'm skeptical of any adventure, even a mini-adventure, that promises to last 1 hour. Especially if that adventure includes any combat. Personally, I don't think I'd ever budget less than 2 hours for D&D.

I think Metamongoose hit the nail on the head, though. The question here is whether this was a good or bad thing for your group (and for you as a DM). If it was a bad thing, then can you identify any specific elements that led to things taking too long?

I think it went long because they had a hard time agreeing on anything. And for a lot of them they hadn't played the game before. 

I've usually had to warp time and space to store things up. 

They don't often roleplay and one of the players talks really slow. It can't be helped. But I think they have a good time. It's just, adventurers league adventures take a long time.  

This happens to me all the time. Nowadays, I create a one-shot adventure that I plan on taking 2 hours, knowing very well that I need to plan to sit down for at least twice the amount of time. 

If you are limited to just one or two hours... are you able to divide the adventure up into multiple gaming sessions (I'm not familiar with the way AL works)?

My players never make it to where I plan on them ending a session, whether it is because a fight takes longer than I thought, they get caught up role playing, or because they have a habit of majorly over thinking the small things in order to cover their keisters from highly unlikely scenarios.

I had a session once where two of the three hours were taken up in combat with a Roper.  My players told me that it was the most boring, tedious session we'd ever done - which is a shame because I enjoyed it :-)

If, however, the session goes on because players can't agree, I think this is awesome!  In fact, as a DM I encourage this disarray in my games to pit PC against PC, whether it is their morals, values or simply order of events.  I believe the key is though, to not allow them to meta-game, that is talk about their approach from a mechanics perspective, and to remain in character to have these disagreements.  I sit in silence until asked a direct question, and some of the ideas and thoughts they have are actually things I hadn't thought of, so I jot them down and weave them into the game at a later date.

As an example, my Warlock and my Rogue who are both chaotic neutral, have just teleported out of a losing combat situation leaving my Wizard and Paladin on the ground at 0 HP!!  The Wizard and Paladin couldn't believe what happened, believing they would somehow be saved.  I now have to figure the next part, but that's okay :-)

I will even reward the chaotic neutral players with a little additional XP because they were in character (however, the Warlocks patron is a Celestial, Lawful Good, so will punish the Warlock for abandoning his party in a time of need, so the XP is a back-handed reward:-) hahaha).

Long and short, if the players are enjoying themselves, you're on a winner - because it's easier to manage your own enjoyment.  The game is a journey, not a destination; there's no rush :-)