The honest answer depends on what you mean by conversation, and that's not evasion — the distance between a short exchange and following a family argument is enormous, and conflating them is why people give up feeling they've failed.
Four different targets
A short exchange. Greetings, how are you, where are you from, something about your family or your work. A patient speaker, one to one.
A real one-to-one conversation. Fifteen minutes about your day, your plans, what you think about something. Still with a speaker making allowances.
Following a group. Several Lebanese people talking to each other at natural speed. Substantially harder than any of the above.
Participating in a group. Joining that conversation in real time.
These aren't points on one line so much as different skills. People reach the first within months and the last after years, which is normal and not a sign of slow progress.
Rough expectations
With regular lessons and practice between them, the first target is a matter of a few months. The second takes most learners something closer to a year of consistent work. The third and fourth come later, and group comprehension is where almost everyone plateaus longest.
Anyone quoting precise timelines is guessing. What varies most isn't aptitude — it's how much you speak, whether you're corrected, and whether you have Lebanese speakers around you.
What makes it faster
Heritage comprehension. If you grew up hearing it, you're not starting where a complete beginner starts — the sound system and a lot of passive vocabulary are already there, and activating them is quicker than building them.
Any Arabic at all. Even MSA. The transfer is real.
Speaking from the first week. The single biggest variable. Learners who delay speaking take considerably longer to get anywhere, whatever else they do.
People to talk to. A partner's family, friends, a community. Lessons plus real conversation beats lessons alone by a wide margin.
What makes it slower
No script, no structure. Lebanese has no standard written form, so self-study materials are inconsistent and thinner than for most languages. This is the main practical argument for a teacher rather than a course.
Everyone switching to English. The universal experience, and the main reason learners stall. It's kindness, and it has to be declined.
Studying MSA when you want to speak. Useful for reading, slow route to conversation.
The part that isn't about time
Most people who can't hold a conversation after a year aren't short of hours. They're short of attempts.
Conversation is a skill built by doing it badly repeatedly, and the learners who get there are the ones who were willing to be clumsy in front of people for a few months. That's the variable, more than talent and more than study time.