Absolutely fantastic time hiking Hallasan! We gave ourselves three days on Jeju just in case the weather was bad, which it turned out being for two of the three days we were there. We booked a reservation online and cancelled the other two days once we knew what the weather was going to look like 24 hours before. We encountered quite a few people that DID not have reservations and could just simply get them at the front desk, but I wouldn't test my luck just in case the amount of permits they give out hit their maximum. We had the timeslot between 8 to 10 AM and started hiking by 9:40 AM. We drove a rental car to the parking lot and there seemed to be a lot space when we started on June 17. The trail started relatively flat for the first few km's and then becomes a mix of trail, roots, and stairs. It's very well maintained and travelled on, but still has a nice sense of isolation and wild feeling considering how busy it is. There's a shelter and washrooms just before you begin the last portion of the summit push. The gate will lock if you do not make it to this point within the allocated timeframe (which changes based on the time of year you are hiking). I don't believe a few parties that we passed would have made it as they were going quite slow. If you believe you are a slow hiker, maybe choose the earlier timeslot to guarantee yourself enough time to summit.
The last portion of the hike was very busy on what seemed like a never ending staircase. There was weirdly a long line-up at the top to take a picture with some sign engraved on a rock? People spent 30 minutes lining up for this instead of actually just looking around and enjoying the views. We didn't get to see much of the crater as the winds were high and it was quite cloudy, but the views everywhere else were stunning. Jeju is so beautiful! Despite how busy the summit area was, we did not feel that the rest of the hike was too crowded as everyone was fairly spread out for the most part.
We hustled pretty hard and managed to summit in 2:35 and made it back down to the parking lot in 2:14. Any questions, reach out on Instagram @brimau5_
Parking: Permit required, Entry fee, Paid, Large lot